Merge pull request #303 from dragos-oancea/switch_core_video-nullptr

[core] scan-build: Dereference of null pointer (loaded from variable 'txt') - switch_img_write_text_img(

src/switch_core_video.c

@@ -2139,6 +2139,10 @@ SWITCH_DECLARE(switch_image_t *) switch_img_write_text_img(int w, int h, switch_
 	switch_image_t *txtimg = NULL;
 	int x = 0, y = 0;
 
+	if (!duptxt) {
+		return NULL;
+	}
+
 	if (strchr(text, ':')) {
 		argc = switch_split(duptxt, ':', argv);