CMakePM: Improve error output handling

This avoids a soft assert for a missing description
and correctly prints the error on the Issues pane.

Change-Id: Ieaeacf404b4a5b323bac215af72877480f627cf8
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/cmakeprojectmanager/cmakeprocess.cpp

@@ -179,7 +179,7 @@ void CMakeProcess::processStandardError()
 
     static QString rest;
     rest = lineSplit(rest, m_process->readAllStandardError(), [this](const QString &s) {
-        m_parser.appendMessage(s, Utils::StdErrFormat);
+        m_parser.appendMessage(s + '\n', Utils::StdErrFormat);
         Core::MessageManager::write(s);
     });
 }