Use another variable assignment with a combined operator for string concatenations

[elfring]

👀 Some source code analysis tools can help to find opportunities for improving software components.
💭 I propose to increase the usage of combined operators accordingly.

diff --git a/pkgdiff.pl b/pkgdiff.pl
index 82ae2f5..06bf614 100644
--- a/pkgdiff.pl
+++ b/pkgdiff.pl
@@ -2038,7 +2038,7 @@ sub showOp($)
         $Op="";
     }
     if($Op) {
-        $Op = $Op." ";
+        $Op .= " ";
     }
     return $Op;
 }