py: mp_call_function_*_protected(): Pass-thru return value if possible.

Return the result of called function. If exception happened, return
MP_OBJ_NULL. Allows to use mp_call_function_*_protected() with callbacks
returning values, etc.

py/runtime.h

@@ -106,8 +106,9 @@ mp_obj_t mp_call_method_n_kw(size_t n_args, size_t n_kw, const mp_obj_t *args);
 mp_obj_t mp_call_method_n_kw_var(bool have_self, size_t n_args_n_kw, const mp_obj_t *args);
 mp_obj_t mp_call_method_self_n_kw(mp_obj_t meth, mp_obj_t self, size_t n_args, size_t n_kw, const mp_obj_t *args);
 // Call function and catch/dump exception - for Python callbacks from C code
-void mp_call_function_1_protected(mp_obj_t fun, mp_obj_t arg);
-void mp_call_function_2_protected(mp_obj_t fun, mp_obj_t arg1, mp_obj_t arg2);
+// (return MP_OBJ_NULL in case of exception).
+mp_obj_t mp_call_function_1_protected(mp_obj_t fun, mp_obj_t arg);
+mp_obj_t mp_call_function_2_protected(mp_obj_t fun, mp_obj_t arg1, mp_obj_t arg2);
 
 typedef struct _mp_call_args_t {
     mp_obj_t fun;

py/runtime_utils.c

@@ -27,22 +27,26 @@
 
 #include "py/runtime.h"
 
-void mp_call_function_1_protected(mp_obj_t fun, mp_obj_t arg) {
+mp_obj_t mp_call_function_1_protected(mp_obj_t fun, mp_obj_t arg) {
     nlr_buf_t nlr;
     if (nlr_push(&nlr) == 0) {
-        mp_call_function_1(fun, arg);
+        mp_obj_t ret = mp_call_function_1(fun, arg);
         nlr_pop();
+        return ret;
     } else {
         mp_obj_print_exception(&mp_plat_print, MP_OBJ_FROM_PTR(nlr.ret_val));
+        return MP_OBJ_NULL;
     }
 }
 
-void mp_call_function_2_protected(mp_obj_t fun, mp_obj_t arg1, mp_obj_t arg2) {
+mp_obj_t mp_call_function_2_protected(mp_obj_t fun, mp_obj_t arg1, mp_obj_t arg2) {
     nlr_buf_t nlr;
     if (nlr_push(&nlr) == 0) {
-        mp_call_function_2(fun, arg1, arg2);
+        mp_obj_t ret = mp_call_function_2(fun, arg1, arg2);
         nlr_pop();
+        return ret;
     } else {
         mp_obj_print_exception(&mp_plat_print, MP_OBJ_FROM_PTR(nlr.ret_val));
+        return MP_OBJ_NULL;
     }
 }