QmlProfiler: Work around QProcess not emitting errorOccurred

When given an empty string as executable and some non-empty arguments
QProcess might emit error() but not errorOccurred(). This was fixed by
2f0ffba638bdb868a810bc0349c240b6b6e172cd in qtbase, but we cannot rely
on that being present, yet. Thus, avoid passing empty strings as
executable.

Change-Id: Ia1bb5ebceb6edeca1e54489d12b838f3cea8851e
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/qmlprofiler/tests/localqmlprofilerrunner_test.cpp

@@ -41,6 +41,7 @@ void LocalQmlProfilerRunnerTest::testRunner()
 {
     Debugger::AnalyzerConnection connection;
     LocalQmlProfilerRunner::Configuration configuration;
+    configuration.debuggee.executable = "\\-/|\\-/";
     configuration.debuggee.environment = Utils::Environment::systemEnvironment();
 
     // should not be used anywhere but cannot be empty