fix for 49063: no sanity checking when setting duplicate. sanity checking

is done for the dup id field, but not for the originating bug id.
now checks to see if the original bug id is valid as well, although i don't
understand how this could get corrupted in the first place

webtools/bugzilla/process_bug.cgi

@@ -528,6 +528,13 @@ SWITCH: for ($::FORM{'knob'}) {
                          "make sense to mark a bug as a duplicate of " .
                          "itself, does it?");
         }
+        my $checkid = trim($::FORM{'id'});
+        SendSQL("SELECT bug_id FROM bugs where bug_id = " .  SqlQuote($checkid));
+        $checkid = FetchOneColumn();
+        if (!$checkid) {
+            PuntTryAgain("The bug id $::FORM{'id'} is invalid. Please reload this bug ".
+                         "and try again.");
+        }
         AppendComment($num, $::FORM{'who'}, "*** Bug $::FORM{'id'} has been marked as a duplicate of this bug. ***");
         if ( Param('strictvaluechecks') ) {
           CheckFormFieldDefined(\%::FORM,'comment');