Explicitly initialize some variables for which we use the default value

This does not change anything in practice because static variables are
initialized implicitly as we need them anyway, but this makes things
clearer and more explicit.

src/highlighting.c

@@ -58,7 +58,7 @@
 #define GEANY_WHITESPACE_CHARS " \t" "!\"#$%&'()*+,-./:;<=>?@[\\]^`{|}~"
 
 
-static gchar *whitespace_chars;
+static gchar *whitespace_chars = NULL;
 
 
 typedef struct
@@ -112,7 +112,7 @@ static struct
 	gint fold_draw_line;
 
 	gchar			*wordchars;
-} common_style_set;
+} common_style_set = { { { 0 } }, 0, 0, 0, NULL };
 
 
 /* For filetypes.common [named_styles] section.