Evaluate unscannable source status once

For some OCUR tuners (i.e. the Ceton), requesting
the status of whether the tuner has an inserted
CableCARD can take 2-3 seconds.  Repeatedly
making that determination at each channel insert
time can result in slow channel update times if
the channel list is large.  Determine the status
only once for the tuner.

mythtv/programs/mythfilldatabase/channeldata.cpp

@@ -176,6 +176,8 @@ void ChannelData::handleChannels(int id, ChannelInfoList *chanlist)
 
     fileprefix += "/";
 
+    bool insertChan = insert_chan(id);  // unscannable source
+
     ChannelInfoList::iterator i = chanlist->begin();
     for (; i != chanlist->end(); ++i)
     {
@@ -365,7 +367,7 @@ void ChannelData::handleChannels(int id, ChannelInfoList *chanlist)
 
             }
         }
-        else if (insert_chan(id)) // Only insert channels for non-scannable sources
+        else if (insertChan) // Only insert channels for non-scannable sources
         {
             int major, minor = 0;
             long long freq = 0;