Check on ATSC major number for suggested channel number

Test on nonzero of the ATSC major number instead of the
minor number when generating a suggested channel number
because the major number is at least 1 but the minor
number can be 0 in an ATSC channel number.

mythtv/libs/libmythtv/channelscan/channelimporter.cpp

@@ -1590,7 +1590,7 @@ QString ChannelImporter::ComputeSuggestedChannelNum(
     QString chan_num = channelFormat
         .arg(chan.m_atscMajorChannel)
         .arg(chan.m_atscMinorChannel);
-    if (chan.m_atscMinorChannel)
+    if (chan.m_atscMajorChannel)
     {
         if (!ChannelUtil::IsConflicting(chan_num, chan.m_sourceId))
             return chan_num;