[gnumeric] GnmStyle: fix precondition for conditional style.

[Morten Welinder <mortenw src gnome org>]

commit 85dce0069233d416365af44c28305e10308857d8
Author: Morten Welinder <terra gnome org>
Date:   Wed Apr 18 21:33:45 2018 -0400

    GnmStyle: fix precondition for conditional style.
    
    (And that's why we have a test suite.)

 ChangeLog    |    3 +++
 src/mstyle.c |    2 +-
 2 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index 7bd8967..acb2407 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,8 @@
 2018-04-18  Morten Welinder  <terra gnome org>
 
+       * src/mstyle.c (gnm_style_get_cond_style): Flip reversed
+       pre-condition.
+
        * src/gui-clipboard.c (gnm_x_claim_clipboard): Offer biff8,
        including LO's weird name for that.  The don't seem to take
        "Biff8" and they don't seem to take Citrix' variant either.
diff --git a/src/mstyle.c b/src/mstyle.c
index b46f874..02c2dac 100644
--- a/src/mstyle.c
+++ b/src/mstyle.c
@@ -2085,7 +2085,7 @@ gnm_style_get_cond_style (GnmStyle const *style, int ix)
        g_return_val_if_fail (elem_is_set (style, MSTYLE_CONDITIONS), NULL);
        g_return_val_if_fail (style->cond_styles != NULL, NULL);
 
-       g_return_val_if_fail (ix < 0 || (unsigned)ix > style->cond_styles->len, NULL);
+       g_return_val_if_fail (ix >= 0 && (unsigned)ix < style->cond_styles->len, NULL);
 
        return g_ptr_array_index (style->cond_styles, ix);
 }