fix Bcg729Config.cmake.in

Bcg729Config.cmake.in

@@ -44,6 +44,9 @@ else()
 	endif()
 endif()
 get_target_property(BCG729_INCLUDE_DIRS ${BCG729_TARGETNAME} INTERFACE_INCLUDE_DIRECTORIES)
+if (NOT BCG729_INCLUDE_DIRS)
+	set (BCG729_INCLUDE_DIRS)
+endif()
 if(LINPHONE_BUILDER_GROUP_EXTERNAL_SOURCE_PATH_BUILDERS)
 	list(INSERT BCG729_INCLUDE_DIRS 0 "${EP_bcg729_INCLUDE_DIR}")
 else()