Add functionality for a FileSource to block acquisition start if it's not ready

Source/Processors/FileReader/FileReader.cpp

@@ -80,7 +80,7 @@ bool FileReader::isReady() /* const */
     }
     else
     {
-        return true;
+        return input->isReady();
     }
 }
 

Source/Processors/FileReader/FileSource.cpp

@@ -140,3 +140,8 @@ bool FileSource::OpenFile (File file)
 
     return fileOpened;
 }
+
+bool FileSource::isReady() const
+{
+	return true;
+}

Source/Processors/FileReader/FileSource.h

@@ -67,6 +67,7 @@ public:
     virtual void processChannelData (int16* inBuffer, float* outBuffer, int channel, int64 numSamples) = 0;
     virtual void seekTo (int64 sample) = 0;
 
+	virtual bool isReady() const;
 
 protected:
     struct RecordInfo