Fix extra new line in the preview window

When a colored text ends at the right end of the window

Fix #3209

src/terminal.go

@@ -1828,13 +1828,15 @@ func (t *Terminal) renderPreviewText(height int, lines []string, lineNo int, unc
 					trimmed, isTrimmed = t.trimRight(trimmed, maxWidth-t.pwindow.X())
 				}
 				str, width := t.processTabs(trimmed, prefixWidth)
-				prefixWidth += width
+				if width > prefixWidth {
+					prefixWidth = width
 					if t.theme.Colored && ansi != nil && ansi.colored() {
 						lbg = ansi.lbg
 						fillRet = t.pwindow.CFill(ansi.fg, ansi.bg, ansi.attr, str)
 					} else {
 						fillRet = t.pwindow.CFill(tui.ColPreview.Fg(), tui.ColPreview.Bg(), tui.AttrRegular, str)
 					}
+				}
 				return !isTrimmed &&
 					(fillRet == tui.FillContinue || t.previewOpts.wrap && fillRet == tui.FillNextLine)
 			})

test/test_go.rb

@@ -2656,6 +2656,23 @@ class TestGoFZF < TestBase
     tmux.send_keys :Enter
     tmux.until { |lines| assert_equal 99, lines.item_count }
   end
+
+  def test_no_extra_newline_issue_3209
+    tmux.send_keys(%(seq 100 | #{FZF} --height 10 --preview-window up,wrap --preview 'printf "─%.0s" $(seq 1 "$((FZF_PREVIEW_COLUMNS - 5))"); printf $"\\e[7m%s\\e[0m" title; echo; echo something'), :Enter)
+    expected = <<~OUTPUT
+      ╭──────────
+      │ ─────────
+      │ something
+      │
+      ╰──────────
+        3
+        2
+      > 1
+        100/100 ─
+      >
+    OUTPUT
+    tmux.until { assert_block(expected, _1) }
+  end
 end
 
 module TestShell