fix(column): add truncated width during estimation for 'statuscolumn'

Problem:    Estimated 'statuscolumn' width estimated is not properly used,
            executing the `w_redr_statuscol` path unnecessarily.
Solution:   Adjust `w_nrwidth` and 'statuscolumn' width before anything
            is actually drawn in a `win_update()`.

test/functional/ui/statuscolumn_spec.lua

@@ -616,4 +616,17 @@ describe('statuscolumn', function()
                                                            |
     ]])
   end)
+
+  it("is only evaluated twice, once to estimate and once to draw", function()
+    command([[
+      let g:stcnr = 0
+      func! Stc()
+        let g:stcnr += 1
+        return '12345'
+      endfunc
+      set stc=%!Stc()
+      norm ggdG
+    ]])
+    eq(2, eval('g:stcnr'))
+  end)
 end)