remove assertion for false assumption; mrb_str_new(0, len) where len > 0 can be used to allocate an unintialized string

src/string.c

@@ -21,7 +21,6 @@
 #include "regex.h"
 #include "st.h"
 #endif //ENABLE_REGEXP
-#include <assert.h>
 
 const char mrb_digitmap[] = "0123456789abcdefghijklmnopqrstuvwxyz";
 
@@ -222,7 +221,7 @@ mrb_value
 mrb_str_new(mrb_state *mrb, const char *p, int len)
 {
   struct RString *s;
-  assert(!(!p && len));
+
   s = str_new(mrb, p, len);
   return mrb_obj_value(s);
 }

src/vm.c

@@ -393,7 +393,7 @@ mrb_run(mrb_state *mrb, struct RProc *proc, mrb_value self)
   mrb_code i;
   int ai = mrb->arena_idx;
   jmp_buf c_jmp;
-  jmp_buf *prev_jmp = NULL;
+  volatile jmp_buf *prev_jmp = NULL;
 
 #ifdef DIRECT_THREADED
   static void *optable[] = {