qt/main: Better file-existence checking within OnMenuRecentFile() and UpdateUITheme()

In OnMenuRecentFile() we don't need to construct a QFileInfo instance
just to check if a file exists, we can just use the static member
function to do that (which Qt's documentation also notes as quicker than
constructing an instance).

In UpdateUITheme(), we just want to try and open the file and check the
success of that operation. Technically speaking, between the existence
check and the open call, the file can be deleted or moved, but still
appear to succeed in code. i.e.

1. Existence check -> Returns true
2. File is moved/deleted
3. Open is called, the return value of which isn't checked
4. Nonsense behavior

This way we combine the existence check and the open into one.

1 files changed, 6 insertions, 8 deletions

diff --git a/src/yuzu/main.cpp b/src/yuzu/main.cpp
index e28679cd1..d0415a7dc 100644
--- a/src/yuzu/main.cpp
+++ b/src/yuzu/main.cpp
@@ -654,9 +654,8 @@ void GMainWindow::OnMenuRecentFile() {
     QAction* action = qobject_cast<QAction*>(sender());
     assert(action);
 
-    QString filename = action->data().toString();
-    QFileInfo file_info(filename);
-    if (file_info.exists()) {
+    const QString filename = action->data().toString();
+    if (QFileInfo::exists(filename)) {
         BootGame(filename);
     } else {
         // Display an error message and remove the file from the list.
@@ -947,15 +946,14 @@ void GMainWindow::UpdateUITheme() {
     QStringList theme_paths(default_theme_paths);
     if (UISettings::values.theme != UISettings::themes[0].second &&
         !UISettings::values.theme.isEmpty()) {
-        QString theme_uri(":" + UISettings::values.theme + "/style.qss");
+        const QString theme_uri(":" + UISettings::values.theme + "/style.qss");
         QFile f(theme_uri);
-        if (!f.exists()) {
-            LOG_ERROR(Frontend, "Unable to set style, stylesheet file not found");
-        } else {
-            f.open(QFile::ReadOnly | QFile::Text);
+        if (f.open(QFile::ReadOnly | QFile::Text)) {
             QTextStream ts(&f);
             qApp->setStyleSheet(ts.readAll());
             GMainWindow::setStyleSheet(ts.readAll());
+        } else {
+            LOG_ERROR(Frontend, "Unable to set style, stylesheet file not found");
         }
         theme_paths.append(QStringList{":/icons/default", ":/icons/" + UISettings::values.theme});
         QIcon::setThemeName(":/icons/" + UISettings::values.theme);