fix(get_portproton_start_command): Check if flatpak command exists before trying to run it

Signed-off-by: Boris Yumankulov <boria138@altlinux.org>

portprotonqt/config_utils.py

@@ -183,6 +183,22 @@ def get_portproton_start_command():
     if not portproton_path:
         return None
 
+    # Check if flatpak command exists before trying to run it
+    try:
+        subprocess.run(
+            ["flatpak", "--version"],
+            capture_output=True,
+            text=True,
+            check=False,
+            timeout=5
+        )
+        flatpak_available = True
+    except FileNotFoundError:
+        flatpak_available = False
+    except Exception:
+        flatpak_available = False
+
+    if flatpak_available:
         try:
             result = subprocess.run(
                 ["flatpak", "list"],