Use 0 rather than NULL for the empty command queue property set

[galekseev]

Drive-by cleanup noticed while reviewing #58, on the line directly above the one that PR changed.

Problem

cl_command_queue_properties is a cl_bitfield, which is a cl_ulong. It is not a pointer type, so initialising it from NULL depends on the null pointer constant converting to an integer. gcc flags this under -Wall, which Makefile enables for every build:

Dispatcher.cpp:140:41: warning: converting to non-pointer type
'cl_command_queue_properties' {aka 'long unsigned int'} from NULL [-Wconversion-null]

Beyond the noise, NULL here reads as "no properties pointer", which is misleading: p is a bitfield of queue property flags, and the intended value is the empty flag set.

Change

 #ifdef PROFANITY_DEBUG
 	cl_command_queue_properties p = CL_QUEUE_PROFILING_ENABLE;
 #else
-	cl_command_queue_properties p = NULL;
+	cl_command_queue_properties p = 0;
 #endif

This matches the #ifdef branch above it, which already assigns a bitfield constant.

Verification

Linux, OpenCL 3.0 headers, gcc 13, built with the project's own flags (-std=c++11 -Wall -O2 -mcmodel=large).

• This was the only -Wconversion-null in the project. Both the release and the -DPROFANITY_DEBUG build now report zero, leaving only the unrelated pre-existing -Waligned-new= note on new Dispatcher::Device.
• The emitted object file is byte-identical before and after (md5 3e19513d758d567d6c1e15acdbfffbb1 either way), so this is a provable no-op at the machine code level.