Remove the .xopp~ backup file after a successful save

This is a combination of 4 commits.

* Fixes #3399 Fixes #1498
  Also fixes that no backup file was created anymore after the first save
  of a file
* Cleanup
* Create a backup file on any save where a file already exists
* Update comment

src/control/Control.cpp

@@ -2406,7 +2406,7 @@ auto Control::saveAs() -> bool {
         return false;
     }
 
-    // no lock needed, this is an uncritically operation
+    // no lock needed, this is an uncritical operation
     this->doc->setCreateBackupOnSave(false);
     return save();
 }

src/control/jobs/SaveJob.cpp

@@ -92,8 +92,9 @@ auto SaveJob::save() -> bool {
 
     Util::clearExtensions(filepath, ".pdf");
     auto const target = fs::path{filepath}.concat(".xopp");
+    auto const createBackup = doc->shouldCreateBackupOnSave();
 
-    if (doc->shouldCreateBackupOnSave()) {
+    if (createBackup) {
         try {
             // Note: The backup must be created for the target as this is the filepath
             // which will be written to. Do not use the `filepath` variable!
@@ -102,7 +103,6 @@ auto SaveJob::save() -> bool {
             g_warning("Could not create backup! Failed with %s", fe.what());
             return false;
         }
-        doc->setCreateBackupOnSave(false);
     }
 
     doc->lock();
@@ -116,6 +116,14 @@ auto SaveJob::save() -> bool {
             g_error("%s", this->lastError.c_str());
         }
         return false;
+    } else if (createBackup) {
+        try {
+            // If a backup was created it can be removed now since no error occured during the save
+            fs::remove(fs::path{target} += "~");
+        } catch (fs::filesystem_error const& fe) { g_warning("Could not delete backup! Failed with %s", fe.what()); }
+    } else {
+        doc->setCreateBackupOnSave(true);
     }
+
     return true;
 }

src/control/xojfile/LoadHandler.cpp

@@ -244,7 +244,7 @@ auto LoadHandler::parseXml() -> bool {
         return false;
     }
 
-    doc.setCreateBackupOnSave(this->fileVersion >= 3);
+    doc.setCreateBackupOnSave(true);
 
     return valid;
 }

src/model/Document.h

@@ -143,7 +143,7 @@ class Document {
     GtkTreeModel* contentsModel = nullptr;
 
     /**
-     *  create a backup before save, because the original file was an older fileversion
+     *  create a backup before save
      */
     bool createBackupOnSave = false;