+ make sure to use valid compression level

src/App/Document.cpp

@@ -945,6 +945,7 @@ bool Document::save (void)
 {
     int compression = App::GetApplication().GetParameterGroupByPath
         ("User parameter:BaseApp/Preferences/Document")->GetInt("CompressionLevel",3);
+    compression = Base::clamp<int>(compression, Z_NO_COMPRESSION, Z_BEST_COMPRESSION);
 
     if (*(FileName.getValue()) != '\0') {
         LastModifiedDate.setValue(Base::TimeInfo::currentDateTimeString());

src/Gui/DlgSettingsDocumentImp.cpp

@@ -23,6 +23,7 @@
 
 #include "PreCompiled.h"
 #include <climits>
+#include <zlib.h>
 
 #include "DlgSettingsDocumentImp.h"
 #include "PrefWidgets.h"
@@ -40,6 +41,8 @@ DlgSettingsDocumentImp::DlgSettingsDocumentImp( QWidget* parent )
 {
     this->setupUi(this);
     prefCountBackupFiles->setMaximum(INT_MAX);
+    prefCompression->setMinimum(Z_NO_COMPRESSION);
+    prefCompression->setMaximum(Z_BEST_COMPRESSION);
 }
 
 /**