Merge pull request #3126 from jbreeden/backtrace_irep_null_check

Null check for irep & initialize loc.lineno

src/backtrace.c

@@ -112,6 +112,8 @@ each_backtrace(mrb_state *mrb, mrb_int ciidx, mrb_code *pc0, each_backtrace_func
     mrb_irep *irep;
     mrb_code *pc;
     
+    loc.lineno = -1;
+
     ci = &mrb->c->cibase[i];
 
     if (!ci->proc) continue;
@@ -128,8 +130,11 @@ each_backtrace(mrb_state *mrb, mrb_int ciidx, mrb_code *pc0, each_backtrace_func
     else {
       pc = pc0;
     }
+    
+    if (irep) {
       loc.filename = mrb_debug_get_filename(irep, (uint32_t)(pc - irep->iseq));
       loc.lineno = mrb_debug_get_line(irep, (uint32_t)(pc - irep->iseq));
+    }
 
     if (loc.lineno == -1) continue;