Move MPEG check to end of content-based detection (#1319)

MPEG::File::isSupported() scans for frame sync bytes that can appear
in other files, causing them to be misidentified as MP3.

This also includes a test with such a file.

Author: DanTheMan827

taglib/fileref.cpp

@@ -246,8 +246,7 @@ namespace
   {
     File *file = nullptr;
 
-    if(MPEG::File::isSupported(stream))
-      file = new MPEG::File(stream, readAudioProperties, audioPropertiesStyle);
+    if(false);
 #ifdef TAGLIB_WITH_VORBIS
     else if(Ogg::Vorbis::File::isSupported(stream))
       file = new Ogg::Vorbis::File(stream, readAudioProperties, audioPropertiesStyle);
@@ -300,6 +299,8 @@ namespace
     else if(Matroska::File::isSupported(stream))
       file = new Matroska::File(stream, readAudioProperties, audioPropertiesStyle);
 #endif
+    else if(MPEG::File::isSupported(stream))
+      file = new MPEG::File(stream, readAudioProperties, audioPropertiesStyle);
 
     // isSupported() only does a quick check, so double check the file here.
 

tests/data/mpeg-sync-flac.flac

@@ -167,6 +167,7 @@ class TestFileRefDetectByContent : public CppUnit::TestFixture
   CPPUNIT_TEST(testSilence44SFlac);
   CPPUNIT_TEST(testSinewaveFlac);
   CPPUNIT_TEST(testZeroSizedPaddingFlac);
+  CPPUNIT_TEST(testFLACWithMPEGSyncBytes);
   // Ogg::Speex::File
   CPPUNIT_TEST(testEmptySpx);
   // Ogg::Opus::File
@@ -326,6 +327,9 @@ class TestFileRefDetectByContent : public CppUnit::TestFixture
   void testZeroSizedPaddingFlac() {
     detectByContent<FLAC::File>("zero-sized-padding.flac");
   }
+  void testFLACWithMPEGSyncBytes() {
+    detectByContent<FLAC::File>("mpeg-sync-flac.flac");
+  }
 
   // -- Ogg::Speex::File --
   void testEmptySpx() { detectByContent<Ogg::Speex::File>("empty.spx"); }