Fix performance problem in fuzzer.

fuzz/fuzz-read-print-write.cpp

@@ -21,17 +21,23 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
 
     image->readMetadata();
     for (auto& md : image->exifData()) {
+      if (md.tagName().substr(0, 2) != "0x") {
         md.print();
         md.print(&image->exifData());
       }
+    }
     for (auto& md : image->iptcData()) {
+      if (md.tagName().substr(0, 2) != "0x") {
         md.print();
         md.print(&image->exifData());
       }
+    }
     for (auto& md : image->xmpData()) {
+      if (md.tagName().substr(0, 2) != "0x") {
         md.print();
         md.print(&image->exifData());
       }
+    }
 
     // Print to a std::ostringstream so that the fuzzer doesn't
     // produce lots of garbage on stdout.