fix request target for URLs with empty path

Author: KurtThiemann

src/Psr7/Message/Request.php

@@ -32,12 +32,16 @@ public function getRequestTarget(): string
             return $this->requestTarget;
         }
 
-        $this->requestTarget = $this->uri->getPath();
+        $target = $this->uri->getPath();
+        if ($target === "") {
+            $target = "/";
+        }
+
         if ($this->uri->getQuery()) {
-            $this->requestTarget .= '?' . $this->uri->getQuery();
+            $target .= '?' . $this->uri->getQuery();
         }
 
-        return $this->requestTarget;
+        return $target;
     }
 
     /**