tag/{aiff,riff}: fix ID3 chunk padding

Apply padding only to the fseek(), not to the chunk size.  This fixes
bogus "failed to read riff chunk" messages when the last chunk has an
odd size.

See http://bugs.musicpd.org/view.php?id=4486

src/tag/Aiff.cxx

@@ -84,14 +84,14 @@ aiff_seek_id3(FILE *file)
 			   underflow when casting to off_t */
 			return 0;
 
-		if (size % 2 != 0)
-			/* pad byte */
-			++size;
-
 		if (memcmp(chunk.id, "ID3 ", 4) == 0)
 			/* found it! */
 			return size;
 
+		if (size % 2 != 0)
+			/* pad byte */
+			++size;
+
 		if (fseek(file, size, SEEK_CUR) != 0)
 			return 0;
 	}

src/tag/Riff.cxx

@@ -82,15 +82,15 @@ riff_seek_id3(FILE *file)
 			   underflow when casting to off_t */
 			return 0;
 
-		if (size % 2 != 0)
-			/* pad byte */
-			++size;
-
 		if (memcmp(chunk.id, "id3 ", 4) == 0 ||
 		    memcmp(chunk.id, "ID3 ", 4) == 0)
 			/* found it! */
 			return size;
 
+		if (size % 2 != 0)
+			/* pad byte */
+			++size;
+
 		if (fseek(file, size, SEEK_CUR) != 0)
 			return 0;
 	}