syncqt: Close ifstream before attempt to remove file

ifstream may block the file descriptor in some operating systems.
Wrap the reading of files in staging directory with extra scope,
to make sure that ifstream closed the descriptor before the removal
attempt. Also make sure that we closed the ifstream explicitly.

Change-Id: I56ef5e9925501912d5cd61e8545f664e0a0d90b8
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
(cherry picked from commit 3115610cfa37b1341392039537299aea4a0b5d93)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/tools/syncqt/main.cpp

@@ -740,9 +740,14 @@ public:
                     == m_producedHeaders.end()) {
                     // Check if header file came from another module as result of the cross-module
                     // deprecation before removing it.
-                    std::ifstream input(entry.path(), std::ifstream::in);
                     std::string firstLine;
-                    std::getline(input, firstLine);
+                    {
+                        std::ifstream input(entry.path(), std::ifstream::in);
+                        if (input.is_open()) {
+                            std::getline(input, firstLine);
+                            input.close();
+                        }
+                    }
                     if (firstLine.find("#ifndef DEPRECATED_HEADER_"
                                        + m_commandLineArgs->moduleName())
                                 == 0