z80: move lbluflw code around

with uflw checks not being in next anymore, we can save ourselves
a forward jump.

blk/282

@@ -1 +1 @@
-VARIABLE lblofl VARIABLE lblexec
+VARIABLE lbluflw VARIABLE lblexec

blk/285

@@ -1,3 +0,0 @@
-lblofl BSET ( abortUnderflow )
-    DE BIN( @ 0x06 ( uflw ) + LDdd(n),
-    JR, L2 FWR ( execute, B287 )

blk/286

@@ -8,7 +8,7 @@ lblnext BSET PC ORG @ 0x1b + ! ( next )
     IFNC, ( SP <= IX? overflow )
         SP PS_ADDR LDdn, IX RS_ADDR LDdn,
         DE BIN( @ 0x13 ( oflw ) + LDdd(n),
-        JR, L3 FWR ( execute, B287 )
+        JR, L2 FWR ( execute, B287 )
     THEN,
     LDA(BC), E A LDrr, BC INCd,
     LDA(BC), D A LDrr, BC INCd,

blk/287

@@ -1,4 +1,4 @@
-lblexec BSET L1 FSET ( B284 ) L2 FSET ( B285 ) L3 FSET ( B286 )
+lblexec BSET L1 FSET ( B284 ) L2 FSET ( B286 )
     ( DE -> wordref )
     ( When we have a BIN( offset, we need to adjust stable
       ABI offsets. )

blk/290

@@ -1,3 +1,6 @@
+lbluflw BSET ( abortUnderflow )
+    DE BIN( @ 0x06 ( uflw ) + LDdd(n),
+    JR, lblexec BWR
 lblchkPS BSET ( chkPS )
 ( Note that you only need to call this in words that push
   back to PSP. If they don't, calling chkPS is redundant with
@@ -9,4 +12,4 @@ lblchkPS BSET ( chkPS )
     SP SUBHLd,
     EXX,
     CNC RETc, ( PS_ADDR >= SP? good )
-    JR, lblofl BWR ( abortUnderflow-B298 )
+    JR, lbluflw BWR

blk/310

@@ -10,6 +10,6 @@ CODE PICK EXX, ( protect BC )
     EXDEHL,
     HL PS_ADDR LDdn,
     DE SUBHLd,
-    IFC, EXX, lblofl @ JP, THEN,
+    IFC, EXX, lbluflw @ JP, THEN,
     BC PUSH,
 EXX, ( unprotect BC ) ;CODE