wayland: Fix one dimensional size constraints

QSize::isEmpty() will return true if either dimension is 0. On the other
hand, given the current language in the spec, it seems like the client
is allowed to set size constraints per dimension.

BUG: 488260

src/wayland/xdgshell.cpp

@@ -347,8 +347,12 @@ void XdgToplevelInterfacePrivate::apply(XdgToplevelCommit *commit)
 
     const auto minSize = commit->minimumSize.value_or(minimumSize);
     const auto maxSize = commit->maximumSize.value_or(maximumSize);
-    if (!minSize.isEmpty() && !maxSize.isEmpty() && (minSize.width() > maxSize.width() || minSize.height() > maxSize.height())) {
-        wl_resource_post_error(resource()->handle, error_invalid_size, "minimum size can't be bigger than the maximum");
+    if ((minSize.width() > 0) && (maxSize.width() > 0) && (minSize.width() > maxSize.width())) {
+        wl_resource_post_error(resource()->handle, error_invalid_size, "minimum width can't be bigger than the maximum width");
+        return;
+    }
+    if ((minSize.height() > 0) && (maxSize.height() > 0) && (minSize.height() > maxSize.height())) {
+        wl_resource_post_error(resource()->handle, error_invalid_size, "minimum height can't be bigger than the maximum height");
         return;
     }
 
@@ -575,12 +579,14 @@ QString XdgToplevelInterface::windowClass() const
 
 QSize XdgToplevelInterface::minimumSize() const
 {
-    return d->minimumSize.isEmpty() ? QSize(0, 0) : d->minimumSize;
+    return QSize(d->minimumSize.width() > 0 ? d->minimumSize.width() : 0,
+                 d->minimumSize.height() > 0 ? d->minimumSize.height() : 0);
 }
 
 QSize XdgToplevelInterface::maximumSize() const
 {
-    return d->maximumSize.isEmpty() ? QSize(INT_MAX, INT_MAX) : d->maximumSize;
+    return QSize(d->maximumSize.width() > 0 ? d->maximumSize.width() : INT_MAX,
+                 d->maximumSize.height() > 0 ? d->maximumSize.height() : INT_MAX);
 }
 
 quint32 XdgToplevelInterface::sendConfigure(const QSize &size, const States &states)