OcdFileImport: Warn about unsupported double line gaps

Double line objects use symbols with boundary lines (e.g., Wide road
symbol). In .ocd files these objects may have gaps in any of the
boundary lines.
Mapper does not support those kind of gaps and thus ignores them when
importing .ocd files.
Issue a warning that gaps in double line objects are not supported.

src/fileformats/ocd_file_import.cpp

@@ -2168,6 +2168,11 @@ void OcdFileImport::fillPathCoords(OcdImportedPathObject *object, bool is_area,
 			// Virtual gaps are not supported
 			addWarningOnce(tr("Virtual gaps in line objects are not supported."));
 		}
+		if (ocd_points[i].x & Ocd::OcdPoint32::FlagLeft || ocd_points[i].y & Ocd::OcdPoint32::FlagRight)
+		{
+			// Double line gaps are not supported
+			addWarningOnce(tr("Gaps in double line objects are not supported."));
+		}
 	}
 
 	// For path objects, create closed parts where the position of the last point is equal to that of the first point