fix ugly stack side effects

tracker.tal

@@ -1,5 +1,5 @@
 ( a blank file )
-( TODO fix ugly stack effects )
+( TODO fix ugly stack effects, add bounds-checking for pattern movemenv )
 %+  { ADD }  %-  { SUB }  %*  { MUL }  %/  { DIV }
 %<  { LTH }  %>  { GTH }  %=  { EQU }  %!  { NEQ }
 %++ { ADD2 } %-- { SUB2 } %** { MUL2 } %// { DIV2 }
@@ -77,7 +77,7 @@ BRK
   #0080 .Screen/x DEO2
   ;get-selected-song-line-address JSR2 ;draw-patterns JSR2
   
-BRK
+RTN
 
 @on-input ( -> )
   .Controller/button DEI
@@ -85,6 +85,7 @@ BRK
   #20 AND ,&down JCN
   BRK
   &up
+    POP
     .tracker/selected-pattern LDZ #01 SUB .tracker/selected-pattern STZ
     ,&end JMP
   &down