Paul Menzel authored Dec 04, 2013 and Jean-Baptiste Kempf committed Dec 29, 2013

Both GCC 4.8.2 and Clang 3.4 warn about a format mismatch in a
comparison.

        libtool: compile:  gcc -DHAVE_CONFIG_H -I. -I.. -I.. -I../src -mno-ms-bitfields -O3 -Wall -D_FILE_OFFSET_BITS=64 -D_LARGEFILE64_SOUR
CE -MT ifo_read.lo -MD -MP -MF .deps/ifo_read.Tpo -c ifo_read.c  -fPIC -DPIC -o .libs/ifo_read.o
        […]
        ifo_read.c: In function 'ifoRead_PTL_MAIT':
        ifo_read.c:1313:34: warning: comparison between pointer and integer [enabled by default]
           if(ifofile->vmgi_mat->ptl_mait == NULL)

        libtool: compile:  clang -DHAVE_CONFIG_H -I. -I.. -I.. -I../src -O3 -Wall -D_FILE_OFFSET_BITS=64 -D_LARGEFILE64_SOURCE -MT ifo_read.
lo -MD -MP -MF .deps/ifo_read.Tpo -c ifo_read.c  -fPIC -DPIC -o .libs/ifo_read.o
        […]
        ifo_read.c:1313:34: warning: comparison between pointer and integer ('uint32_t' (aka 'unsigned int') and 'void *')
          if(ifofile->vmgi_mat->ptl_mait == NULL)
             ~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^  ~~~~

Fix this by using the integer 0 instead of `NULL`.