[Diagnostics] Improve insertion location check when handling a missing argument

Author: janbaig

lib/Sema/CSDiagnostics.cpp

@@ -5338,6 +5338,8 @@ bool MissingArgumentsFailure::diagnoseSingleMissingArgument() const {
     // fn(argX, argY):
     //   fn(argX, argY[, argMissing])
     if (args->empty()) {
+      if (!args->getRParenLoc().isValid())
+        return false;  
       insertLoc = args->getRParenLoc();
     } else if (position != 0) {
       auto argPos = std::min(args->size(), position) - 1;
@@ -5377,9 +5379,6 @@ bool MissingArgumentsFailure::diagnoseSingleMissingArgument() const {
     }
   }
 
-  if (insertLoc.isInvalid())
-    return false;
-
   // If we are trying to insert a trailing closure but the parameter
   // corresponding to the missing argument doesn't support a trailing closure,
   // don't provide a Fix-It.