Fix 11285: FN: zerodiv (#4448)

* Fix 11285: FN: zerodiv

* Format

Author: pfultz2

lib/valueflow.cpp

@@ -7578,7 +7578,7 @@ struct ContainerExpressionAnalyzer : ExpressionAnalyzer {
         if (isLikelyStreamRead(isCPP(), tok->astParent()))
             return Action::Invalid;
         if (astIsContainer(tok) && isContainerSizeChanged(tok, getSettings()))
-            return Action::Invalid;
+            return read | Action::Invalid;
         return read;
     }
 };

test/testvalueflow.cpp

@@ -2661,6 +2661,26 @@ class TestValueFlow : public TestFixture {
                "}";
         ASSERT_EQUALS(true, testValueOfXKnown(code, 6U, 1));
         ASSERT_EQUALS(false, testValueOfXKnown(code, 6U, 2));
+
+        code = "int f() {\n"
+               "    std::string a;\n"
+               "    std::string b=\"42\";\n"
+               "    std::swap(b, a);\n"
+               "    int x = b.size();\n"
+               "    return x;\n"
+               "}\n";
+        ASSERT_EQUALS(true, testValueOfXKnown(code, 6U, 0));
+        ASSERT_EQUALS(false, testValueOfXKnown(code, 6U, 2));
+
+        code = "int f() {\n"
+               "    std::string a;\n"
+               "    std::string b=\"42\";\n"
+               "    std::swap(b, a);\n"
+               "    int x = a.size();\n"
+               "    return x;\n"
+               "}\n";
+        ASSERT_EQUALS(true, testValueOfXKnown(code, 6U, 2));
+        ASSERT_EQUALS(false, testValueOfXKnown(code, 6U, 0));
     }
 
     void valueFlowAfterCondition() {