The type definition of `sptr_t' depends on the compiler and C++ standard
being used, see external/scintilla/include/Scintilla.h and Scintilla's
upstream commit "Change definition of uptr_t and sptr_t to use
standardised types and headers"[0].

On OpenBSD 6.5/amd64, Clang 7.0.1 defaults to C++14,  thus `NULL' is
defined as `nullptr' so assigning it to `sptr_t' aka. `long' will fail.

Fix all callers (to the legacy Scintilla code) by using zero:

	/WndProc(/s,NULL,0,
	/glBindBuffer(/s,NULL,0,
	/glUseProgram(/s,NULL,0,

0: https://github.com/mirror/scintilla/commit/91bbc3c933d663b3bc9f4572cf1ed02d77922fde


Signed-off-by: Gargaj <gargaj@conspiracy.hu>