Ensure GRASS plugin CMake extra includes macro works for all versions

Author: dakcarto

cmake/FindGRASS.cmake

@@ -18,7 +18,8 @@ MACRO (CHECK_GRASS_EXTRA_INCLUDE_DIRS GRASS_VERSION)
      AND "${GRASS${GRASS_VERSION}_EXTRA_INCLUDE_DIRS}" STREQUAL "")
 
     FILE(READ ${GRASS_INCLUDE_DIR${GRASS_VERSION}}/Make/Platform.make _platformfile)
-    STRING(REGEX MATCH "INCLUDE_DIRS *= [^\n]*" _config_includes "${_platformfile}")
+    STRING(REGEX MATCH "INCLUDE_DIRS *= *[^\n]*" _config_includes "${_platformfile}")
+    SET(_extra_includes "")
     IF(NOT "${_config_includes}" STREQUAL "")
       STRING(REGEX REPLACE "INCLUDE_DIRS *= *([^\n]*)" "\\1" _extra_includes "${_config_includes}")
     ENDIF()