ProtobufScalarJsonSerializers: fix overflowed return value

Restructure the limits check to be more compact by separating the
invariant from the variant. The latter is extracted into a constexpr
lambda check.

Fix the overflow by checking the ok flag and return a default
initialized T.

Coverity-Id: 479421
Change-Id: Ia50fcba5de1335c2a26478d10f89b2d9c5696c4b
Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/protobuf/protobufscalarjsonserializers_p.h

@@ -173,22 +173,19 @@ T deserialize(const QJsonValue &value, bool &ok)
 
     // For types that "smaller" than qint64 we need to check if the value fits its limits range
     if constexpr (sizeof(T) != sizeof(qint64)) {
-        if (ok) {
+        constexpr auto Limits = []() {
             if constexpr (std::is_same_v<T, QtProtobuf::sfixed32>
-                          || std::is_same_v<T, QtProtobuf::int32>) {
+                          || std::is_same_v<T, QtProtobuf::int32>)
-                using limits = std::numeric_limits<qint32>;
+                return std::numeric_limits<qint32>{};
-                ok = raw >= limits::min() && raw <= limits::max();
+            else if constexpr (std::is_same_v<T, QtProtobuf::fixed32>)
-            } else if constexpr (std::is_same_v<T, QtProtobuf::fixed32>) {
+                return std::numeric_limits<quint32>{};
-                using limits = std::numeric_limits<quint32>;
+            else
-                ok = raw >= limits::min() && raw <= limits::max();
+                return std::numeric_limits<T>{};
-            } else {
+        }();
-                using limits = std::numeric_limits<T>;
+        ok = ok && (raw >= Limits.min() && raw <= Limits.max());
-                ok = raw >= limits::min() && raw <= limits::max();
-            }
-        }
     }
 
-    return T(raw);
+    return ok ? T(raw) : T{};
 }
 
 template <typename T, if_json_int64<T> = true>