Address staabm review: native return type, early return, reorder $this check

- Add native return type to resolveCallUserFuncCalleeReflection
- Add early return null after constant strings block since a type
  cannot be both constant string and constant array
- Move $this check to be first inside the loop

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: phpstan-bot

src/Analyser/ExprHandler/FuncCallHandler.php

@@ -885,6 +885,8 @@ private function resolveCallUserFuncCalleeReflection(FuncCall $innerFuncCall, Mu
 			if ($this->reflectionProvider->hasFunction($funcName, $scope)) {
 				return $this->reflectionProvider->getFunction($funcName, $scope);
 			}
+
+			return null;
 		}
 
 		$constantArrays = $callbackType->getConstantArrays();