Fix possible uninitialised value dereference if jq_init() fails

If jq_init() fails, goto out would try to free input_state which is
uninitialised. I initialised input_state to NULL to fix the problem.

I also fixed jq_util_input_init() not handling OOM errors by returning
NULL, and added code to make jq exit cleanly if it returns NULL. The
code base is filled with these kinds of problems, but this one was easy
to fix, so might as well fix it now...

Ref: #2934 (comment)

Reported-By: Klemens Nanni <kn@openbsd.org>

src/main.c

@@ -310,6 +310,7 @@ int umain(int argc, char* argv[]) {
 int main(int argc, char* argv[]) {
 #endif
   jq_state *jq = NULL;
+  jq_util_input_state *input_state = NULL;
   int ret = JQ_OK_NO_OUTPUT;
   int compiled = 0;
   int parser_flags = 0;
@@ -336,15 +337,20 @@ int main(int argc, char* argv[]) {
 
   jq = jq_init();
   if (jq == NULL) {
-    perror("malloc");
+    perror("jq_init");
     ret = JQ_ERROR_SYSTEM;
     goto out;
   }
 
   int dumpopts = JV_PRINT_INDENT_FLAGS(2);
   const char* program = 0;
 
-  jq_util_input_state *input_state = jq_util_input_init(NULL, NULL); // XXX add err_cb
+  input_state = jq_util_input_init(NULL, NULL); // XXX add err_cb
+  if (input_state == NULL) {
+    perror("jq_util_input_init");
+    ret = JQ_ERROR_SYSTEM;
+    goto out;
+  }
 
   int further_args_are_strings = 0;
   int further_args_are_json = 0;

src/util.c

@@ -226,10 +226,12 @@ jq_util_input_state *jq_util_input_init(jq_util_msg_cb err_cb, void *err_cb_data
     err_cb_data = stderr;
   }
   jq_util_input_state *new_state = jv_mem_calloc(1, sizeof(*new_state));
-  new_state->err_cb = err_cb;
-  new_state->err_cb_data = err_cb_data;
-  new_state->slurped = jv_invalid();
-  new_state->current_filename = jv_invalid();
+  if(new_state) {
+    new_state->err_cb = err_cb;
+    new_state->err_cb_data = err_cb_data;
+    new_state->slurped = jv_invalid();
+    new_state->current_filename = jv_invalid();
+  }
 
   return new_state;
 }