Add reb_simulation_try_create() and clarify reb_simulation_create() allocation failure behavior.

Author: yuanzui-cf

src/rebound.c

@@ -380,12 +380,18 @@ int reb_simulation_reset_function_pointers(struct reb_simulation* const r){
 }
 
 struct reb_simulation* reb_simulation_create(){
+    struct reb_simulation* r = reb_simulation_try_create();
+    if (r == NULL) reb_exit("Memory allocation failed.");
+    return r;
+}
+
+struct reb_simulation* reb_simulation_try_create(){
     struct reb_simulation* r = calloc(1,sizeof(struct reb_simulation));
+    if (r == NULL) return NULL;
     reb_simulation_init(r);
     return r;
 }
 
-
 void reb_simulation_copy_with_messages(struct reb_simulation* r_copy,  struct reb_simulation* r, enum reb_simulation_binary_error_codes* warnings){
     char* bufp;
     size_t sizep;

src/rebound.h

@@ -701,8 +701,10 @@ struct reb_simulation {
 
 // Simulation life cycle
 
-// Allocates memory for reb_simulation and initializes it.
+// Allocates memory for reb_simulation and initializes it. Fatal on allocation failure.
 DLLEXPORT struct reb_simulation* reb_simulation_create(void);
+// Attempts to allocate memory for reb_simulation and initializes it. Returns NULL on allocation failure.
+DLLEXPORT struct reb_simulation* reb_simulation_try_create(void);
 // Create a simulation object from a file. Set snapshot=-1 to load last snapshot.
 DLLEXPORT struct reb_simulation* reb_simulation_create_from_file(char* filename, int64_t snapshot);
 // Create a simulation object from a simulationarchive. Set snapshot=-1 to load last snapshot.