MIPS: Fix BC_ISNEXT fallback path.

Thanks to RT-RK.com.

src/vm_mips.dasc

@@ -3619,24 +3619,24 @@ static void build_ins(BuildCtx *ctx, BCOp op, int defop)
   case BC_ISNEXT:
     |  // RA = base*8, RD = target (points to ITERN)
     |  addu RA, BASE, RA
-    |  lw TMP0, -24+HI(RA)
-    |  lw CFUNC:TMP1, -24+LO(RA)
-    |   lw TMP2, -16+HI(RA)
-    |    lw TMP3, -8+HI(RA)
+    |    srl TMP0, RD, 1
+    |  lw CARG1, -24+HI(RA)
+    |  lw CFUNC:CARG2, -24+LO(RA)
+    |    addu TMP0, PC, TMP0
+    |   lw CARG3, -16+HI(RA)
+    |   lw CARG4, -8+HI(RA)
     |  li AT, LJ_TFUNC
-    |  bne TMP0, AT, >5
-    |.  addiu TMP2, TMP2, -LJ_TTAB
-    |  lbu TMP1, CFUNC:TMP1->ffid
-    |  addiu TMP3, TMP3, -LJ_TNIL
-    |   srl TMP0, RD, 1
-    |  or TMP2, TMP2, TMP3
-    |  addiu TMP1, TMP1, -FF_next_N
-    |   addu TMP0, PC, TMP0
-    |  or TMP1, TMP1, TMP2
-    |  bnez TMP1, >5
-    |.  lui TMP2, (-(BCBIAS_J*4 >> 16) & 65535)
+    |  bne CARG1, AT, >5
+    |.   lui TMP2, (-(BCBIAS_J*4 >> 16) & 65535)
+    |  lbu CARG2, CFUNC:CARG2->ffid
+    |   addiu CARG3, CARG3, -LJ_TTAB
+    |   addiu CARG4, CARG4, -LJ_TNIL
+    |   or CARG3, CARG3, CARG4
+    |  addiu CARG2, CARG2, -FF_next_N
+    |  or CARG2, CARG2, CARG3
+    |  bnez CARG2, >5
+    |.  lui TMP1, 0xfffe
     |  addu PC, TMP0, TMP2
-    |  lui TMP1, 0xfffe
     |  ori TMP1, TMP1, 0x7fff
     |  sw r0, -8+LO(RA)			// Initialize control var.
     |  sw TMP1, -8+HI(RA)
@@ -3646,7 +3646,7 @@ static void build_ins(BuildCtx *ctx, BCOp op, int defop)
     |  li TMP3, BC_JMP
     |   li TMP1, BC_ITERC
     |  sb TMP3, -4+OFS_OP(PC)
-    |   addu PC, TMP0, TMP2
+    |    addu PC, TMP0, TMP2
     |  b <1
     |.  sb TMP1, OFS_OP(PC)
     break;