rimage: fix CSE header detection check when re-signing

Test the outcome of the scan instead of the loop index,
so the check no longer depends on the loop bound, and
align the message with the one used by verify_image().

Signed-off-by: Adrian Bonislawski <adrian.bonislawski@intel.com>

Author: abonislawski

tools/rimage/src/manifest.c

@@ -1791,8 +1791,12 @@ int resign_image(struct image *image)
 		}
 	}
 
-	if (i >= size) {
-		fprintf(stderr, "error: didn't found header marker %d\n", i);
+	/* the scan stops a full marker before the end, so a trailing partial word
+	 * leaves the loop index below the size; test the result of the scan itself
+	 */
+	if (!image->fw_image) {
+		fprintf(stderr, "error: could not find valid CSE header $CPD in %s\n",
+			image->in_file);
 		ret = -EINVAL;
 		goto out;
 	}