Git: Avoid crash when reloading files

Explicitly reset the document when the document gets closed.

Task-number: QTCREATORBUG-30824
Change-Id: I4fb3d6fd6041990e5b8b4f6b7c4fd9ebc62f5a4a
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: André Hartmann <aha_1980@gmx.de>

src/plugins/git/instantblame.cpp

@@ -166,6 +166,13 @@ void InstantBlame::setup()
 
     connect(EditorManager::instance(), &EditorManager::currentEditorChanged,
             this, setupBlameForEditor);
+    connect(EditorManager::instance(), &EditorManager::documentClosed,
+            this, [this](IDocument *doc) {
+        if (m_document != doc)
+            return;
+        disconnect(m_documentChangedConn);
+        m_document = nullptr;
+    });
 }
 
 // Porcelain format of git blame output