Debugger: Fix command setting active frame

Using this command without prefix and with the 0n decimal prefix
resulted in unreliable frame selection. Last chance is the hexadecimal
prefix.

Change-Id: I935d88849eb541534d4f311ac6059bcd35aee62c
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/debugger/cdb/cdbengine.cpp

@@ -1210,7 +1210,7 @@ void CdbEngine::activateFrame(int index)
     stackHandler()->setCurrentIndex(index);
     gotoLocation(frame);
     if (m_pythonVersion > 0x030000)
-        runCommand({".frame " + QString::number(index), NoFlags});
+        runCommand({".frame 0x" + QString::number(index, 16), NoFlags});
     updateLocals();
 }