Add input guards to fortio_fread_buffer for parity with resdata PR #1189

Reject null buffers and negative buffer sizes up front, returning false instead of risking a null dereference or hitting util_abort. The buffer-overflow protection from the upstream fix is already present via #14144; these two input-validation guards are the remaining delta.

ThirdParty/Ert/lib/ecl/fortio.c

@@ -550,6 +550,11 @@ static int fortio_fread_record(fortio_type *fortio , char *buffer , int max_reco
 */
 
 bool fortio_fread_buffer(fortio_type * fortio, char * buffer , int buffer_size) {
+  if (buffer == NULL && buffer_size != 0)
+    return false;
+  if (buffer_size < 0)
+    return false;
+
   int total_bytes_read = 0;
 
   while (true) {