Fix ANDImm flag updater

For nonzero values we were leaving Z=prev, which is wrong when Z=0
because the AND result might be zero.  Now if Z=1 we leave it alone,
but if Z=0 we now set it to Z=?.

Test 1003-flags-and-branches was testing for the (incorrect)
behavior, so we're now running into a BRK.  This is fine.

Asm65/OpDef.cs

@@ -667,10 +667,12 @@ namespace Asm65 {
         }
         private static StatusFlags FlagUpdater_ANDImm(StatusFlags flags, int immVal,
                 ref StatusFlags condBranchTakenFlags) {
-            // AND #00 --> Z=1, else Z=prev
+            // AND #00 --> Z=1, else if Z=0 then Z=?
             // AND #7f --> N=0, else N=prev
             if (immVal == 0) {
-                flags.Z = 1;
+                flags.Z = 1;    // acc is now zero
+            } else if (flags.Z == 0) {
+                flags.Z = TriState16.INDETERMINATE; // acc *might* now be zero
             }
             bool hiBitClear;
             if (immVal >= 0) {

SourceGen/RuntimeData/Apple/DOS33.sym65

@@ -31,6 +31,7 @@ RWTS_TRACK_NUM  @ $b7ec     ;track number (0 - 34)
 RWTS_SECTOR_NUM @ $b7ed     ;sector number (0-15)
 RWTS_DCT        @ $b7ee 2   ;pointer to Device Characteristics Table
 RWTS_BUF        @ $b7f0 2   ;pointer to data buffer for READ/WRITE
+;RWTS_UNUSED    @ $b7f2
 RWTS_PARTIAL_COUNT @ $b7f3  ;byte count for partial sector
 RWTS_CMD_CODE   @ $b7f4     ;0=seek, 1=read, 2=write, 4=format
 RWTS_ERR_CODE   @ $b7f5     ;err code (when carry set)

SourceGen/SGTestData/Expected/1003-flags-and-branches_64tass.S

@@ -154,8 +154,8 @@ _L10AB  lda     #$00
 _L10B3  lda     #$ff
         and     #$7f
         bne     _L10BB
+        brk
 
-        .byte   $00
         .byte   $db
 
 _L10BB  bpl     _L10BF

SourceGen/SGTestData/Expected/1003-flags-and-branches_Merlin32.S

@@ -149,8 +149,8 @@ L105F    sep   #$80
 :L10B3   lda   #$ff
          and   #$7f
          bne   :L10BB
+         brk
 
-         dfb   $00
          dfb   $db
 
 :L10BB   bpl   :L10BF

SourceGen/SGTestData/Expected/1003-flags-and-branches_acme.S

@@ -154,8 +154,8 @@ L105F   sep     #$80
 @L10B3  lda     #$ff
         and     #$7f
         bne     @L10BB
+        brk
 
-        !byte   $00
         !byte   $db
 
 @L10BB  bpl     @L10BF

SourceGen/SGTestData/Expected/1003-flags-and-branches_cc65.S

@@ -155,8 +155,8 @@ L105F:   sep     #$80
 @L10B3:  lda     #$ff
          and     #$7f
          bne     @L10BB
+         brk
 
-         .byte   $00
          .byte   $db
 
 @L10BB:  bpl     @L10BF