Fix fileinfo.xml generation in mytharchivehelper

Plugin mytharchive:
When ffmpeg cannot determine the codec of the provided stream,
the whole buffer provided by `avcodec_string` is taken in the function
`getFileInfo` to create an xml entry. Cleanup this buffer by removing
'\0' characters. Otherwise, the return codec in the xml sequence will
hold 256 zeros and mythburn.py fails to read this xml file.

Refs #609

mythplugins/mytharchive/mytharchivehelper/mytharchivehelper.cpp

@@ -1967,7 +1967,7 @@ static int getFileInfo(const QString& inFile, const QString& outFile, int lenMet
 #else
                 QStringList param = QString::fromStdString(buf).split(',', Qt::SkipEmptyParts);
 #endif
-                QString codec = param[0].remove("Video:", Qt::CaseInsensitive);
+                QString codec = param[0].remove("Video:", Qt::CaseInsensitive).remove(QChar::Null);
                 QDomElement stream = doc.createElement("video");
                 stream.setAttribute("streamindex", i);
                 stream.setAttribute("ffmpegindex", ffmpegIndex++);
@@ -2098,7 +2098,7 @@ static int getFileInfo(const QString& inFile, const QString& outFile, int lenMet
 #else
                 QStringList param = QString::fromStdString(buf).split(',', Qt::SkipEmptyParts);
 #endif
-                QString codec = param[0].remove("Audio:", Qt::CaseInsensitive);
+                QString codec = param[0].remove("Audio:", Qt::CaseInsensitive).remove(QChar::Null);
 
                 QDomElement stream = doc.createElement("audio");
                 stream.setAttribute("streamindex", i);
@@ -2172,7 +2172,7 @@ static int getFileInfo(const QString& inFile, const QString& outFile, int lenMet
             {
                 QDomElement stream = doc.createElement("data");
                 stream.setAttribute("streamindex", i);
-                stream.setAttribute("codec", QString::fromStdString(buf));
+                stream.setAttribute("codec", QString::fromStdString(buf).remove(QChar::Null));
                 streams.appendChild(stream);
 
                 break;