Ignore capture cards without video source

Ignore the capture cards that are not connected to a video source.
This is for most users a situation that never happens, and there are
messages given by the backend at startup when there are capture cards
without a video source as this might indicate a configuration error.
Howver, test systems can have many capture cards of which only a few
are to be used simultaneously and disconnecting the video source is
the easiest way to temporarily disable a capture card.

mythtv/libs/libmythtv/cardutil.cpp

@@ -2249,6 +2249,7 @@ std::vector<uint> CardUtil::GetConflictingInputs(uint inputid)
         "JOIN inputgroup ig ON ig.inputgroupid = g.inputgroupid "
         "JOIN capturecard c ON c.cardid = ig.cardinputid "
         "                      AND c.cardid <> :INPUTID2 "
+        "                      AND c.sourceid > 0 "
         "ORDER BY c.cardid");
 
     query.bindValue(":INPUTID1", inputid);

mythtv/programs/mythbackend/scheduler.cpp

@@ -5831,6 +5831,7 @@ bool Scheduler::InitInputInfoMap(void)
 
     query.prepare("SELECT cardid, parentid, schedgroup "
                   "FROM capturecard "
+                  "WHERE sourceid > 0 "
                   "ORDER BY cardid");
     if (!query.exec())
     {