proton: Fix a couple simple crashes

Fixes a crash when no verb is provided due to accessing a nonexistent index in `sys.argv`.
Allows the `STEAM_COMPAT_CLIENT_INSTALL_PATH` environment variable to not be set.

proton

@@ -810,7 +810,9 @@ class CompatData:
                 os.symlink("/", self.prefix_dir + "/dosdevices/z:")
 
             # collect configuration info
-            steamdir = os.environ["STEAM_COMPAT_CLIENT_INSTALL_PATH"]
+            steamdir = os.environ.get("STEAM_COMPAT_CLIENT_INSTALL_PATH")
+            if steamdir is None:
+                steamdir = ""
 
             use_wined3d = "wined3d" in g_session.compat_config
             use_dxvk_dxgi = not use_wined3d and \
@@ -892,10 +894,11 @@ class CompatData:
                                ("GameOverlayRenderer64.dll", "GameOverlayRenderer64.dll"),
                                ("SteamService.exe", "steam.exe"),
                                ("Steam.dll", "Steam.dll")]
-                for (src,tgt) in filestocopy:
-                    srcfile = steamdir + '/legacycompat/' + src
-                    if os.path.isfile(srcfile):
-                        try_copy(srcfile, steam_dir + tgt, prefix=self.prefix_dir, track_file=tracked_files, link_debug=True)
+                if steamdir:
+                    for (src,tgt) in filestocopy:
+                        srcfile = steamdir + '/legacycompat/' + src
+                        if os.path.isfile(srcfile):
+                            try_copy(srcfile, steam_dir + tgt, prefix=self.prefix_dir, track_file=tracked_files, link_debug=True)
 
                 filestocopy = [("steamclient64.dll", "steamclient64.dll"),
                                ("GameOverlayRenderer.dll", "GameOverlayRenderer.dll"),
@@ -996,7 +999,7 @@ class CompatData:
 
             # add Steam ffmpeg libraries to path
             use_ffmpeg = "PROTON_NO_STEAM_FFMPEG" not in os.environ or not nonzero(os.environ["PROTON_NO_STEAM_FFMPEG"])
-            if use_ffmpeg and 'nosteamffmpeg' not in g_session.compat_config:
+            if use_ffmpeg and 'nosteamffmpeg' not in g_session.compat_config and steamdir:
                 prepend_to_env_str(g_session.env, ld_path_var, steamdir + "/ubuntu12_64/video/:" + steamdir + "/ubuntu12_32/video/", ":")
 
 def comma_escaped(s):
@@ -1647,10 +1650,13 @@ if __name__ == "__main__":
     if g_proton.missing_default_prefix():
         g_proton.make_default_prefix()
 
-    g_session.init_session(sys.argv[1] != "runinprefix")
+    g_session.init_session(len(sys.argv) < 2 or sys.argv[1] != "runinprefix")
 
     #determine mode
     rc = 0
+    if len(sys.argv) < 2:
+        log("Need a verb.")
+        sys.exit(1)
     if sys.argv[1] == "run":
         #start target app
         setup_game_dir_drive()
@@ -1674,7 +1680,7 @@ if __name__ == "__main__":
         path = subprocess.check_output([g_proton.wine_bin, "winepath", sys.argv[2]], env=g_session.env, stderr=g_session.log_file)
         sys.stdout.buffer.write(path)
     else:
-        log("Need a verb.")
+        log("Bad verb.")
         sys.exit(1)
 
     sys.exit(rc)