Fix protect exception for print error message

src/error.c

@@ -490,6 +490,8 @@ mrb_no_method_error(mrb_state *mrb, mrb_sym id, mrb_value args, char const* fmt,
   mrb_exc_raise(mrb, exc);
 }
 
+void mrb_core_init_printabort(void);
+
 int
 mrb_core_init_protect(mrb_state *mrb, void (*body)(mrb_state *, void *), void *opaque)
 {
@@ -502,7 +504,13 @@ mrb_core_init_protect(mrb_state *mrb, void (*body)(mrb_state *, void *), void *o
     body(mrb, opaque);
     err = 0;
   } MRB_CATCH(&c_jmp) {
-    mrb->exc = NULL;
+    if (mrb->exc) {
+      mrb_p(mrb, mrb_obj_value(mrb->exc));
+      mrb->exc = NULL;
+    }
+    else {
+      mrb_core_init_printabort();
+    }
   } MRB_END_EXC(&c_jmp);
 
   mrb->jmp = prev_jmp;

src/print.c

@@ -7,24 +7,48 @@
 #include <mruby.h>
 #include <mruby/string.h>
 #include <mruby/variable.h>
+#include <mruby/error.h>
+#include <string.h>
 
 #ifndef MRB_DISABLE_STDIO
+static void
+printcstr(const char *str, size_t len, FILE *stream)
+{
+  if (str) {
+    fwrite(str, len, 1, stream);
+    putc('\n', stream);
+  }
+}
+
 static void
 printstr(mrb_value obj, FILE *stream)
 {
   if (mrb_string_p(obj)) {
-    fwrite(RSTRING_PTR(obj), RSTRING_LEN(obj), 1, stream);
-    putc('\n', stream);
+    printcstr(RSTRING_PTR(obj), RSTRING_LEN(obj), stream);
   }
 }
 #else
+# define printcstr(str, len, stream) (void)0
 # define printstr(obj, stream) (void)0
 #endif
 
+void
+mrb_core_init_printabort(void)
+{
+  static const char *str = "Failed mruby core initialization";
+  printcstr(str, strlen(str), stdout);
+}
+
 MRB_API void
 mrb_p(mrb_state *mrb, mrb_value obj)
 {
-  printstr(mrb_inspect(mrb, obj), stdout);
+  if (mrb_type(obj) == MRB_TT_EXCEPTION && mrb_obj_ptr(obj) == mrb->nomem_err) {
+    static const char *str = "Out of memory";
+    printcstr(str, strlen(str), stdout);
+  }
+  else {
+    printstr(mrb_inspect(mrb, obj), stdout);
+  }
 }
 
 MRB_API void