Fix Filesystem::isLocalPath including windows checks on linux

src/Composer/Util/Filesystem.php

@@ -628,9 +628,15 @@ class Filesystem
      */
     public static function isLocalPath($path)
     {
+        // on windows, \\foo indicates network paths so we exclude those from local paths, however it is unsafe
+        // on linux as file:////foo (which would be a network path \\foo on windows) will resolve to /foo which could be a local path
+        if (Platform::isWindows()) {
             return Preg::isMatch('{^(file://(?!//)|/(?!/)|/?[a-z]:[\\\\/]|\.\.[\\\\/]|[a-z0-9_.-]+[\\\\/])}i', $path);
         }
 
+        return Preg::isMatch('{^(file://|/|/?[a-z]:[\\\\/]|\.\.[\\\\/]|[a-z0-9_.-]+[\\\\/])}i', $path);
+    }
+
     /**
      * @param string $path
      *