ulwgl_run: refactor logic for PROTONPATH

- Prioritize checking the Proton version first instead of including the logic as apart of fetching the Proton. This way, we also allow clients to assign other Proton forks such as GE-Proton instead of strictly ULWGL-Proton.

ulwgl_run.py

@@ -120,25 +120,29 @@ def check_env(
 
     env["WINEPREFIX"] = os.environ["WINEPREFIX"]
 
-    if "PROTONPATH" not in os.environ:
-        os.environ["PROTONPATH"] = ""
-        get_ulwgl_proton(env)
-    elif (
-        Path("~/.local/share/Steam/compatibilitytools.d/" + os.environ["PROTONPATH"])
+    # Proton Version
+    if (
+        "PROTONPATH" in os.environ
+        and os.environ["PROTONPATH"]
+        and Path(
+            "~/.local/share/Steam/compatibilitytools.d/" + os.environ["PROTONPATH"]
+        )
         .expanduser()
         .is_dir()
     ):
-        env["PROTONPATH"] = (
-            Path("~/.local/share/Steam/compatibilitytools.d/")
-            .expanduser()
+        log.debug(msg("Proton version selected", Level.DEBUG))
+        os.environ["PROTONPATH"] = (
+            Path("~/.local/share/Steam/compatibilitytools.d")
             .joinpath(os.environ["PROTONPATH"])
+            .expanduser()
             .as_posix()
         )
-    elif not Path(os.environ["PROTONPATH"]).expanduser().is_dir():
+
+    if "PROTONPATH" not in os.environ:
         os.environ["PROTONPATH"] = ""
         get_ulwgl_proton(env)
-    else:
-        env["PROTONPATH"] = os.environ["PROTONPATH"]
+
+    env["PROTONPATH"] = os.environ["PROTONPATH"]
 
     # If download fails/doesn't exist in the system, raise an error
     if not os.environ["PROTONPATH"]: