Update testvalueflow.cpp

Author: chrchr-github

test/testvalueflow.cpp

@@ -1837,6 +1837,14 @@ class TestValueFlow : public TestFixture {
         ASSERT_EQUALS(1U, values.size());
         ASSERT_EQUALS(3 * settings.platform.sizeof_int, values.back().intvalue);
         ASSERT_EQUALS_ENUM(ValueFlow::Value::ValueKind::Known, values.back().valueKind);
+
+        code = "int f(char c) {\n" // #15037
+               "    return sizeof(+c);\n"
+               "}\n";
+        values = tokenValues(code, "( +");
+        ASSERT_EQUALS(1U, values.size());
+        ASSERT_EQUALS(settings.platform.sizeof_int, values.back().intvalue);
+        ASSERT_EQUALS_ENUM(ValueFlow::Value::ValueKind::Known, values.back().valueKind);
     }
 
     void valueFlowComma()