Fix BLI_path test of BLI_path_frame_strip.

Ensure that returned string buffer is always properly initialized with
NULL char...

source/blender/blenlib/intern/path_util.c

@@ -881,6 +881,7 @@ bool BLI_path_frame_get(char *path, int *r_frame, int *r_numdigits)
 
 void BLI_path_frame_strip(char *path, char *r_ext)
 {
+	*r_ext = '\0';
 	if (*path == '\0') {
 		return;
 	}