Try to read multiple images in fuzzer

fuzz/fuzz_targets/decode_image.rs

@@ -15,5 +15,13 @@ fuzz_target!(|data: &[u8]| {
 
     decoder = decoder.with_limits(limits);
     
-    let _ = decoder.read_image();
+    loop {
+        if let Err(_) = decoder.read_image() {
+            break;
+        }
+
+        if !decoder.more_images() {
+            break;
+        }
+    }
 });