Fix drawing terminator, round usec

mandel.s

@@ -1253,11 +1253,15 @@ loop:
     txa
     tay
     lda (strptr),y
-    bmi padding
+    pha ; save the char for terminator check
+    and #$7f ; strip the high bit (terminator)
     tay
     lda char_map,y
     sta textbuffer + col,x
     inx
+
+    pla
+    bmi padding
     jmp loop
 
 padding:
@@ -1749,12 +1753,10 @@ update_status:
     jsr FLD1R
     jsr FMUL
 
-    ; @fixme
-    ; round to integer
-    ; for some reason this gives bad results?
-    ;clc
-    ;jsr FPI
-    ;jsr IFP
+    ; round (down) to integer
+    jsr FPI
+    clc
+    jsr IFP
 
     ; convert to ASCII in INBUFF
     jsr FASC