Docker/Linux: Fix outputForRunInShell

... in case there is embedded NUL in the output.

Change-Id: Ic899bcf8d01cceed4ea6e16d4991fb80b7ac70ca
Reviewed-by: Christian Stenger <christian.stenger@qt.io>
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/remotelinux/linuxdevice.cpp

@@ -270,7 +270,7 @@ public:
         if (pos >= 0)
             output = output.left(pos);
         DEBUG("CHOPPED2 " << output);
-        return QString::fromUtf8(output);
+        return QString::fromUtf8(output, output.size());
     }
 
     bool isRunning() const { return m_shell; }