Use wxString::empty() function calls to determine if string is empty in wxPG.

Use this dedicated function instead of explicitly check if wxString::length() returns non-zero value.

src/propgrid/manager.cpp

@@ -982,7 +982,7 @@ wxPropertyGridPage* wxPropertyGridManager::InsertPage( int index,
 
     if ( !label.empty() )
     {
-        wxASSERT_MSG( !pageObj->m_label.length(),
+        wxASSERT_MSG( pageObj->m_label.empty(),
                       wxT("If page label is given in constructor, empty label must be given in AddPage"));
         pageObj->m_label = label;
     }

src/propgrid/property.cpp

@@ -2299,7 +2299,7 @@ void wxPGProperty::DoAddChild( wxPGProperty* prop, int index,
 
 void wxPGProperty::DoPreAddChild( int index, wxPGProperty* prop )
 {
-    wxASSERT_MSG( prop->GetBaseName().length(),
+    wxASSERT_MSG( !prop->GetBaseName().empty(),
                   "Property's children must have unique, non-empty "
                   "names within their scope" );
 

src/propgrid/propgridpagestate.cpp

@@ -1692,7 +1692,7 @@ bool wxPropertyGridPageState::PrepareToAddItem( wxPGProperty* property,
 
     if ( scheduledParent && !scheduledParent->IsCategory() )
     {
-        wxASSERT_MSG( property->GetBaseName().length(),
+        wxASSERT_MSG( !property->GetBaseName().empty(),
                       "Property's children must have unique, non-empty names within their scope" );
     }
 

src/propgrid/props.cpp

@@ -95,7 +95,7 @@ wxString wxStringProperty::ValueToString( wxVariant& value,
         // Value stored in m_value is non-editable, non-full value
         if ( (argFlags & wxPG_FULL_VALUE) ||
              (argFlags & wxPG_EDITABLE_VALUE) ||
-             !s.length() )
+             s.empty() )
         {
             // Calling this under incorrect conditions will fail
             wxASSERT_MSG( argFlags & wxPG_VALUE_IS_CURRENT,