gitwidget: disconnect living git processes at destr

When the GitWidget is destroyed while there is still any git QProcess
arround, the exit signal will be delivered to lambda with invalid
closure.

Function calls looks something like this:
* ~GitWidget
* ~QWidget
* QWidget::deleteChildren
* ~QProcess
* emit QProcess::finished
* call finished lambda referencing already destroyed GitWidget

See: !430

addons/project/gitwidget.cpp

@@ -251,6 +251,14 @@ GitWidget::~GitWidget()
     if (m_cancelHandle) {
         m_cancelHandle->kill();
     }
+
+    // if there are any living processes, disconnect them now before gitwidget get destroyed
+    for (QObject *child : children()) {
+        QProcess *p = qobject_cast<QProcess *>(child);
+        if (p) {
+            disconnect(p, nullptr, nullptr, nullptr);
+        }
+    }
 }
 
 void GitWidget::setDotGitPath()