Fix for lack of input focus clicking on no icon

Detail:
  If R0=valid window handle, R1<0 (not an icon) and R4=-1 then R4 is internally set to 'invisible caret' to ensure that we get the full input focus event and visible cues.
  Ref: https://www.riscosopen.org/forum/forums/5/topics/14945?page=2#posts-97886
Admin:
  Submission for Clipboard Support bounty.

s/CnPCaret

@@ -335,6 +335,7 @@ wscp_workarea
 
         ; upcaret corrupts R11
         CMP     R4,#-1
+        MOVEQ   R4,#crf_invisible       ; if no flags supplied, make the caret invisible
         TSTNE   R4,#crf_ghostcaret
         ADREQL  R11,caretdata
         ADRNEL  R11,ghostcaretdata