[gtksourceview] sourceiter: check movements before continuing

[Christian Hergert <chergert src gnome org>]

commit 1af4ba9a9e3918c095e4446018c6f92afe82a88c
Author: Christian Hergert <chergert redhat com>
Date:   Mon Sep 16 20:58:46 2019 -0700

    sourceiter: check movements before continuing
    
    When moving through the buffer, we can have a situation where the edges
    of the buffer are invisible, and therefore _is_start() will return FALSE
    but the movement we performed did nothing (and left us at the visual
    position of 0:0 or -1:-1).
    
    This fixes that situation by checking the return value of those
    movements and bailing as we would otherwise.
    
    Fixes #76

 gtksourceview/gtksourceiter.c | 44 +++++++++++++++++++++++++++++++++++--------
 1 file changed, 36 insertions(+), 8 deletions(-)
---
diff --git a/gtksourceview/gtksourceiter.c b/gtksourceview/gtksourceiter.c
index afe94ba0..538f209f 100644
--- a/gtksourceview/gtksourceiter.c
+++ b/gtksourceview/gtksourceiter.c
@@ -68,14 +68,21 @@ _gtk_source_iter_forward_full_word_end (GtkTextIter *iter)
 
        while (g_unichar_isspace (gtk_text_iter_get_char (&pos)))
        {
-               gtk_text_iter_forward_visible_cursor_position (&pos);
+               if (!gtk_text_iter_forward_visible_cursor_position (&pos))
+               {
+                       break;
+               }
        }
 
        while (!gtk_text_iter_is_end (&pos) &&
               !g_unichar_isspace (gtk_text_iter_get_char (&pos)))
        {
                non_blank_found = TRUE;
-               gtk_text_iter_forward_visible_cursor_position (&pos);
+
+               if (!gtk_text_iter_forward_visible_cursor_position (&pos))
+               {
+                       break;
+               }
        }
 
        if (non_blank_found)
@@ -97,7 +104,11 @@ _gtk_source_iter_backward_full_word_start (GtkTextIter *iter)
        while (!gtk_text_iter_is_start (&pos))
        {
                prev = pos;
-               gtk_text_iter_backward_visible_cursor_position (&prev);
+
+               if (!gtk_text_iter_backward_visible_cursor_position (&prev))
+               {
+                       break;
+               }
 
                if (!g_unichar_isspace (gtk_text_iter_get_char (&prev)))
                {
@@ -110,7 +121,11 @@ _gtk_source_iter_backward_full_word_start (GtkTextIter *iter)
        while (!gtk_text_iter_is_start (&pos))
        {
                prev = pos;
-               gtk_text_iter_backward_visible_cursor_position (&prev);
+
+               if (!gtk_text_iter_backward_visible_cursor_position (&prev))
+               {
+                       break;
+               }
 
                if (g_unichar_isspace (gtk_text_iter_get_char (&prev)))
                {
@@ -197,11 +212,17 @@ _gtk_source_iter_forward_extra_natural_word_end (GtkTextIter *iter)
        {
                if (gtk_text_iter_get_char (iter) == '_')
                {
-                       gtk_text_iter_forward_visible_cursor_position (iter);
+                       if (!gtk_text_iter_forward_visible_cursor_position (iter))
+                       {
+                               break;
+                       }
                }
                else if (gtk_text_iter_starts_word (iter))
                {
-                       gtk_text_iter_forward_visible_word_end (iter);
+                       if (!gtk_text_iter_forward_visible_word_end (iter))
+                       {
+                               break;
+                       }
                }
                else
                {
@@ -243,7 +264,11 @@ _gtk_source_iter_backward_extra_natural_word_start (GtkTextIter *iter)
        while (!gtk_text_iter_is_start (iter))
        {
                GtkTextIter prev = *iter;
-               gtk_text_iter_backward_visible_cursor_position (&prev);
+
+               if (!gtk_text_iter_backward_visible_cursor_position (&prev))
+               {
+                       break;
+               }
 
                if (gtk_text_iter_get_char (&prev) == '_')
                {
@@ -251,7 +276,10 @@ _gtk_source_iter_backward_extra_natural_word_start (GtkTextIter *iter)
                }
                else if (gtk_text_iter_ends_word (iter))
                {
-                       gtk_text_iter_backward_visible_word_start (iter);
+                       if (!gtk_text_iter_backward_visible_word_start (iter))
+                       {
+                               break;
+                       }
                }
                else
                {