DynASM: Improve validation of local backwards relocations.

dynasm/dasm_x86.h

@@ -213,7 +213,8 @@ void dasm_put(Dst_DECL, int start, ...)
       case DASM_REL_LG:
       case DASM_IMM_LG:
 	n = *p++; pl = D->lglabels + n;
-	if (n <= 246) { CKPL(lg, LG); goto putrel; }  /* Bkwd rel or global. */
+	/* Bkwd rel or global. */
+	if (n <= 246) { CK(n>=10||*pl<0, RANGE_LG); CKPL(lg, LG); goto putrel; }
 	pl -= 246; n = *pl;
 	if (n < 0) n = 0;  /* Start new chain for fwd rel if label exists. */
 	goto linkrel;