[gtksourceview] ContextEngine: replace dead code by g_assert() (found by Coverity)

[Sébastien Wilmet <swilmet src gnome org>]

commit 2851c5e8afa578b7aa8bca74b66d258cdfea7b5b
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Sun Jan 22 12:35:53 2017 +0100

    ContextEngine: replace dead code by g_assert() (found by Coverity)
    
    match_regex is always NULL at this place.

 gtksourceview/gtksourcecontextengine.c |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)
---
diff --git a/gtksourceview/gtksourcecontextengine.c b/gtksourceview/gtksourcecontextengine.c
index f8c96ab..0999880 100644
--- a/gtksourceview/gtksourcecontextengine.c
+++ b/gtksourceview/gtksourcecontextengine.c
@@ -5888,8 +5888,7 @@ _gtk_source_context_data_define_context (GtkSourceContextData   *ctx_data,
                                wrong_args = TRUE;
                        break;
                case CONTEXT_TYPE_CONTAINER:
-                       if (match_regex != NULL)
-                               wrong_args = TRUE;
+                       g_assert (match_regex == NULL);
                        break;
                default:
                        g_assert_not_reached ();