RunControl: Reset future interface before in startEngine()

This fixes an infinite loop for the following use case:
  1. Menu: Analyze > Clang Static Analzyer
  2. When finished, click "Re-run this run-configuration" in the
     application output pane

m_progress was left in the isFinished() state and the next run to
startEngine() called analyzeNextFile() which returned immediately.

Change-Id: I8acf4f03dfc1d7f81034610828f6fb707655bd52
Sanity-Review: Sanity Bot <srv.sanitybot@digia.com>
Reviewed-by: Christian Kandeler <christian.kandeler@theqtcompany.com>

plugins/clangstaticanalyzer/clangstaticanalyzerruncontrol.cpp

@@ -211,6 +211,7 @@ bool ClangStaticAnalyzerRunControl::startEngine()
 
     // Set up progress information
     using namespace Core;
+    m_progress = QFutureInterface<void>();
     FutureProgress *futureProgress
         = ProgressManager::addTask(m_progress.future(), tr("Analyzing"), "ClangStaticAnalyzer");
     futureProgress->setKeepOnFinish(FutureProgress::HideOnFinish);