Merge pull request #607 from ubfx/filerecord_header

Only write .sqriq header once when the first samples are written

sdrbase/dsp/filerecord.cpp

@@ -117,7 +117,6 @@ void FileRecord::startRecording()
         m_recordOn = true;
         m_recordStart = true;
         m_byteCount = 0;
-        writeHeader();
     }
 }