Fix crash in LoopAnalyzer (#4888)

Author: chrchr-github

lib/checkstl.cpp

@@ -2781,7 +2781,7 @@ namespace {
             if (var->declarationId() == loopVar->varId())
                 return false;
             const Scope* scope = var->scope();
-            return scope->isNestedIn(bodyTok->scope());
+            return scope && scope->isNestedIn(bodyTok->scope());
         }
 
     private:

test/teststl.cpp

@@ -5476,6 +5476,23 @@ class TestStl : public TestFixture {
               true);
         ASSERT_EQUALS("[test.cpp:2]: (style) Consider using std::all_of or std::none_of algorithm instead of a raw loop.\n",
                       errout.str());
+
+        check("class C {\n"
+              "private:\n"
+              "    QString s;\n"
+              "public:\n"
+              "    C(QString);\n"
+              "private slots:\n"
+              "    void f() {\n"
+              "        QVERIFY(QDir(s).exists());\n"
+              "    }\n"
+              "    void f(const QStringList& d) {\n"
+              "        for (QString f : d)\n"
+              "          QDir(s);\n"
+              "    }\n"
+              "};\n",
+              true);
+        ASSERT_EQUALS("", errout.str());
     }
 
     void invalidContainer() {