[gnumeric] nlsolve: use a g_assert for hinting gcc about number of vars.

[Morten Welinder <mortenw src gnome org>]

commit c53474627319c103bd8a9cdd3e8199e220b3a194
Author: Morten Welinder <terra gnome org>
Date:   Mon Jul 9 19:58:36 2018 -0400

    nlsolve: use a g_assert for hinting gcc about number of vars.
    
    Kills a warning.

 plugins/nlsolve/gnm-nlsolve.c | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/plugins/nlsolve/gnm-nlsolve.c b/plugins/nlsolve/gnm-nlsolve.c
index 396f12094..dcf207800 100644
--- a/plugins/nlsolve/gnm-nlsolve.c
+++ b/plugins/nlsolve/gnm-nlsolve.c
@@ -321,6 +321,9 @@ rosenbrock_iter (GnmNlsolve *nl)
        gnm_float eps = gnm_pow2 (-16);
        int safety = 0;
 
+       // Give gcc a few hints.
+       g_assert (n >= 0 && n < (1<<20));
+       
        if (nl->tentative) {
                nl->tentative--;
                if (nl->tentative == 0) {