[Fix] Remove CMake Warning (dev) in external/assimp/CMakeLists.txt with mis-matching arguments for logical block

CMakeLists.txt

@@ -183,7 +183,7 @@ OPTION(ASSIMP_BUILD_ZLIB
 
 IF ( NOT ASSIMP_BUILD_ZLIB )
     find_package(ZLIB)
-ENDIF(ASSIMP_BUILD_ZLIB)
+ENDIF( NOT ASSIMP_BUILD_ZLIB )
 
 IF( NOT ZLIB_FOUND )
   message(STATUS "compiling zlib from souces")