Initialize chanid in mythtranscode

Static analysis (scan-build) detects that the variable
chanid could be used without initialization.  This is
actually a false positive, since the use is protected
by the found_chanid variable, but initializing the
variable should be benign, and eliminates that static
analysis detected issue.
(cherry picked from commit 49617bc)

Signed-off-by: Stuart Morgan <smorgan@mythtv.org>

Fixes #11571

mythtv/programs/mythtranscode/main.cpp

@@ -160,7 +160,7 @@ namespace
 
 int main(int argc, char *argv[])
 {
-    uint chanid;
+    uint chanid = 0;
     QDateTime starttime;
     QString infile, outfile;
     QString profilename = QString("autodetect");