Check inputs

As reported by Coverity Scan

src/mat4.c

@@ -126,8 +126,13 @@ Mat_VarWrite4(mat_t *mat, const matvar_t *matvar)
 
  if ( NULL == mat || NULL == matvar )
  return MATIO_E_BAD_ARGUMENT;
- if ( NULL == matvar->name || matvar->rank != 2 )
+ if ( NULL == matvar->name || matvar->rank != 2 || NULL == matvar->data )
  return MATIO_E_OUTPUT_BAD_DATA;
+ if ( matvar->class_type == MAT_C_SPARSE ) {
+ const mat_sparse_t *sparse = (const mat_sparse_t *)matvar->data;
+ if ( sparse->njc == 0 )
+ return MATIO_E_OUTPUT_BAD_DATA;
+ }
 
  switch ( matvar->data_type ) {
  case MAT_T_DOUBLE:

src/mat5.c

@@ -4903,15 +4903,14 @@ Mat_VarWrite5(mat_t *mat, matvar_t *matvar, int compress)
  int nBytes, nzmax = 0;
  mat_off_t start = 0, end = 0;
 
- if ( NULL == mat )
+ if ( NULL == mat || NULL == matvar )
  return MATIO_E_BAD_ARGUMENT;
+ if ( NULL == matvar->name || NULL == matvar->data )
+ return MATIO_E_OUTPUT_BAD_DATA;
 
  /* FIXME: SEEK_END is not Guaranteed by the C standard */
  (void)fseeko((FILE *)mat->fp, 0, SEEK_END); /* Always write at end of file */
 
- if ( NULL == matvar || NULL == matvar->name )
- return MATIO_E_BAD_ARGUMENT;
-
 #if HAVE_ZLIB
  if ( compress == MAT_COMPRESSION_NONE ) {
 #else

src/mat73.c

@@ -3271,6 +3271,8 @@ Mat_VarWrite73(mat_t *mat, matvar_t *matvar, int compress)
 
  if ( NULL == mat || NULL == matvar )
  return MATIO_E_BAD_ARGUMENT;
+ if ( NULL == matvar->name || NULL == matvar->data )
+ return MATIO_E_OUTPUT_BAD_DATA;
 
  matvar->compression = (enum matio_compression)compress;