checkSignConversion: dont warn for + and -

lib/checktype.cpp

@@ -225,7 +225,7 @@ void CheckType::checkSignConversion()
     for (std::size_t i = 0; i < functions; ++i) {
         const Scope * scope = symbolDatabase->functionScopes[i];
         for (const Token* tok = scope->classStart->next(); tok != scope->classEnd; tok = tok->next()) {
-            if (!tok->isArithmeticalOp())
+            if (!tok->isArithmeticalOp() || Token::Match(tok,"+|-"))
                 continue;
 
             unsigned int size = 0;

test/testtype.cpp

@@ -116,6 +116,13 @@ private:
               "}\n"
               "void f2() { f1(-4); }");
         ASSERT_EQUALS("[test.cpp:1]: (warning) Suspicious code: sign conversion of x in calculation, even though x can have a negative value\n", errout.str());
+
+        // Dont warn for + and -
+        check("void f1(int x) {"
+              "  a = x + 5U;\n"
+              "}\n"
+              "void f2() { f1(-4); }");
+        ASSERT_EQUALS("", errout.str());
     }
 };