Fix closing a pattern file.

Because we did not properly cleared VAbstractPattern class state Valentina thought that after closing the pattern file we still have unsaved changes.

(cherry picked from commit a907ab03ce)

src/libs/ifc/xml/vabstractpattern.cpp

@@ -604,6 +604,7 @@ void VAbstractPattern::Clear()
     m_watermarkPath.clear();
     m_companyName.clear();
     m_units = Unit::LAST_UNIT_DO_NOT_USE;
+    modified = false;
 }
 
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