Get rid of trivial compiler warning.

Namely

    In file included from src/numpy_cpp.h:17,
                     from src/py_converters.h:17,
                     from src/ft2font_wrapper.cpp:4:
    src/ft2font_wrapper.cpp: In function ‘int PyFT2Font_init(PyFT2Font*, PyObject*, PyObject*)’:
    src/py_exceptions.h:31:26: warning: converting to non-pointer type ‘int’ from NULL [-Wconversion-null]
       31 |         return (errorcode);                                                  \
          |                          ^
    src/py_exceptions.h:68:27: note: in expansion of macro ‘CALL_CPP_FULL’
       68 | #define CALL_CPP(name, a) CALL_CPP_FULL(name, a, , NULL)
          |                           ^~~~~~~~~~~~~
    src/ft2font_wrapper.cpp:572:5: note: in expansion of macro ‘CALL_CPP’
      572 |     CALL_CPP("FT2Font->set_kerning_factor", (self->x->set_kerning_factor(kerning_factor)));
          |

(multiple times).

Author: anntzer

src/py_exceptions.h

@@ -63,9 +63,9 @@ class exception : public std::exception
         return (errorcode);                                                  \
     }
 
-#define CALL_CPP_CLEANUP(name, a, cleanup) CALL_CPP_FULL(name, a, cleanup, NULL)
+#define CALL_CPP_CLEANUP(name, a, cleanup) CALL_CPP_FULL(name, a, cleanup, 0)
 
-#define CALL_CPP(name, a) CALL_CPP_FULL(name, a, , NULL)
+#define CALL_CPP(name, a) CALL_CPP_FULL(name, a, , 0)
 
 #define CALL_CPP_INIT(name, a) CALL_CPP_FULL(name, a, , -1)