Fire the .valet-env environment var detection earlier

To support smarter detection of static-file detection and allow Valet to mutate the URI for externally-hosted assets (save bandwidth and local storage etc), detecting any custom-inserted environment variables needs to happen slightly sooner in the execution cycle.

Discovered this issue when troubleshooting #729 and #247. While they have other workarounds, this PR simplifies things, and potentially makes custom drivers slightly easier too ... when the use-case applies.

server.php

@@ -121,6 +121,13 @@ function valet_default_site_path($config)
     $_SERVER['HTTP_X_FORWARDED_HOST'] = $_SERVER['HTTP_X_ORIGINAL_HOST'];
 }
 
+/**
+ * Attempt to load server environment variables.
+ */
+$valetDriver->loadServerEnvironmentVariables(
+    $valetSitePath, $siteName
+);
+
 /**
  * Allow driver to mutate incoming URL.
  */
@@ -135,13 +142,6 @@ function valet_default_site_path($config)
     return $valetDriver->serveStaticFile($staticFilePath, $valetSitePath, $siteName, $uri);
 }
 
-/**
- * Attempt to load server environment variables.
- */
-$valetDriver->loadServerEnvironmentVariables(
-    $valetSitePath, $siteName
-);
-
 /**
  * Attempt to dispatch to a front controller.
  */