[gnome-music] Check that Query.music_folder and Query.download_folder are not empty

[Vadim Rutkovsky <vrutkovsky src gnome org>]

commit 9a2fd5aa1dab9c4ef8e1f9e7d70bc04ff9f5ef15
Author: Vadim Rutkovsky <vrutkovs redhat com>
Date:   Mon Aug 24 17:20:44 2015 +0200

    Check that Query.music_folder and Query.download_folder are not empty
    
    https://bugzilla.gnome.org/show_bug.cgi?id=753258

 INSTALL             |    4 ++--
 gnomemusic/query.py |    6 ++++--
 2 files changed, 6 insertions(+), 4 deletions(-)
---
diff --git a/INSTALL b/INSTALL
index 007e939..2099840 100644
--- a/INSTALL
+++ b/INSTALL
@@ -12,8 +12,8 @@ without warranty of any kind.
 Basic Installation
 ==================
 
-   Briefly, the shell commands `./configure; make; make install' should
-configure, build, and install this package.  The following
+   Briefly, the shell command `./configure && make && make install'
+should configure, build, and install this package.  The following
 more-detailed instructions are generic; see the `README' file for
 instructions specific to this package.  Some packages provide this
 `INSTALL' file but do not implement all of the features documented
diff --git a/gnomemusic/query.py b/gnomemusic/query.py
index b4fa8aa..b9ab38e 100644
--- a/gnomemusic/query.py
+++ b/gnomemusic/query.py
@@ -48,13 +48,15 @@ class Query():
     def __init__(self):
         try:
             Query.music_folder = GLib.get_user_special_dir(GLib.UserDirectory.DIRECTORY_MUSIC)
-        except TypeError:
+            assert Query.music_folder is not None
+        except (TypeError, AssertionError):
             logger.warn("XDG Music dir is not set")
             return
 
         try:
             Query.download_folder = GLib.get_user_special_dir(GLib.UserDirectory.DIRECTORY_DOWNLOAD)
-        except TypeError:
+            assert Query.download_folder is not None
+        except (TypeError, AssertionError):
             logger.warn("XDG Download dir is not set")
             return