cleanup: code simplification in get_master_score

Merge two different condition leading to the same result together.
This make the code actually simpler to understand and removes a
step.

script/pgsqlms

@@ -360,12 +360,10 @@ sub _get_master_score {
 
     $score = qx{ $CRM_MASTER --quiet --get-value $node_arg 2> /dev/null };
 
-    return '' unless $? == 0;
+    return '' unless $? == 0 and defined $score;
 
     chomp $score;
 
-    $score = '' unless defined $score;
-
     return $score;
 }