lp8 loader: Ensure that lp8 path macro is defined.

Previously, the macro `8680/lua-pack/path`, which contains the path of
the lp8 to be loaded, may have been undefined at the call site of the
macro `NX_LOAD_LP8` if the macro `NX_LP8` was defined as `1.1`,
resulting in a preprocessor error (“macro/file "8680/lua-pack/path" is
missing at lua/lp8/_main.cfg:16”).

lua/lp8/_main.cfg

@@ -53,6 +53,10 @@
 
 #ifver NX_LP8 == 1.1
 	#ifdef NX_LP8_FOUND
+		#ifndef 8680/lua-pack/path
+			#define 8680/lua-pack/path
+{NX_LP8_PATH}#enddef
+		#endif
 		{NX_LOAD_LP8}
 	#else
 		#define NX_LP8_FAIL