Fix a bug handling high-color themes

Thank goodness I caught this before releasing CSApprox 2.0!  Two
misplaced lines meant that it would crap all over already 256 color
themes, like inkpot.vim and vividchalk.vim, because they cleared the old
cterm colors before the test that made sure that none of the old cterm
colors were over 15.

plugin/CSApprox.vim

@@ -628,9 +628,6 @@ function! s:CSApproxImpl()
   " Get the current highlight colors
   let highlights = s:Highlights()
 
-  call s:FixupGuiInfo(highlights)
-  call s:FixupCtermInfo(highlights)
-
   let hinums = keys(highlights)
 
   " Make sure that the script is not already 256 color by checking to make
@@ -651,6 +648,9 @@ function! s:CSApproxImpl()
     endif
   endfor
 
+  call s:FixupGuiInfo(highlights)
+  call s:FixupCtermInfo(highlights)
+
   " We need to set the Normal group first so 'bg' and 'fg' work as colors
   call sort(hinums, "s:SortNormalFirst")