Fixed an access violation when compiled with Visual Studio upon releasing the OpenCL program

CHANGELOG

@@ -6,6 +6,7 @@ Development (next version)
 - Improved the performance potential by adding a second tunable GEMM kernel with 2D register tiling
 - Re-added a local memory size constraint to the tuners
 - Updated and reorganised the CLBlast documentation
+- Fixed an access violation when compiled with Visual Studio upon releasing the OpenCL program
 - Various minor fixes and enhancements
 - Added tuned parameters for various devices (see doc/tuning.md)
 - Added non-BLAS level-1 routines:

src/clpp11.hpp

@@ -442,7 +442,9 @@ class Program {
   // Source-based constructor with memory management
   explicit Program(const Context &context, const std::string &source):
       program_(new cl_program, [](cl_program* p) {
-        if (*p) { CheckErrorDtor(clReleaseProgram(*p)); }
+        #ifndef _MSC_VER // 'clReleaseProgram' caused an access violation with Visual Studio
+          if (*p) { CheckErrorDtor(clReleaseProgram(*p)); }
+        #endif
         delete p;
       }) {
     const char *source_ptr = &source[0];