Null check for irep & initialize loc.lineno

src/backtrace.c

@@ -108,6 +108,8 @@ each_backtrace(mrb_state *mrb, mrb_int ciidx, mrb_code *pc0, each_backtrace_func
 
   for (i = ciidx; i >= 0; i--) {
     struct backtrace_location_raw loc;
+    loc.lineno = -1;
+    
     mrb_callinfo *ci;
     mrb_irep *irep;
     mrb_code *pc;
@@ -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;