Detect ISO files from file contents if extensions are wrong.

On older Android versions (that still support Android Storage
Framework), filenames are not always preserved in Content URIs, they can
look like .../msf:342 and things like that. So identify a few more file
types by content if filename identification fails.

Core/Loaders.h

@@ -37,6 +37,7 @@ enum class IdentifiedFileType {
 
 	UNKNOWN_BIN,
 	UNKNOWN_ELF,
+	UNKNOWN_ISO,
 
 	// Try to reduce support emails...
 	ARCHIVE_RAR,