patch 8.2.3706: text property highlighting is used on Tab

Problem:    Text property highlighting is used on Tab.
Solution:   Only set in_linebreak when not on a Tab. (closes #9242)

src/drawline.c

@@ -2046,7 +2046,7 @@ win_line(
 
 		    c_extra = mb_off > 0 ? MB_FILLER_CHAR : ' ';
 		    c_final = NUL;
-		    if (n_extra > 0)
+		    if (n_extra > 0 && c != TAB)
 			in_linebreak = TRUE;
 		    if (VIM_ISWHITE(c))
 		    {

src/testdir/dumps/Test_prop_after_tab.dump

@@ -0,0 +1,10 @@
+| +0&#ffffff0@6> |[+0#ffffff16#e000002|x+0#0000000#ffffff0@2|]| @61
+|~+0#4040ff13&| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+| +0#0000000&@56|1|,|1|-|8| @8|A|l@1| 

src/testdir/test_textprop.vim

@@ -1633,6 +1633,24 @@ func Test_prop_in_linebreak()
   call delete('XscriptPropLinebreak')
 endfunc
 
+func Test_prop_after_tab()
+  CheckRunVimInTerminal
+
+  let lines =<< trim END
+    set breakindent linebreak breakat+=]
+    call setline(1, "\t[xxx]")
+    call prop_type_add('test', #{highlight: 'ErrorMsg'})
+    call prop_add(1, 2, #{length: 1, type: 'test'})
+  END
+  call writefile(lines, 'XscriptPropAfterTab')
+  let buf = RunVimInTerminal('-S XscriptPropAfterTab', #{rows: 10})
+  call TermWait(buf)
+  call VerifyScreenDump(buf, 'Test_prop_after_tab', {})
+
+  call StopVimInTerminal(buf)
+  call delete('XscriptPropAfterTab')
+endfunc
+
 " Buffer number of 0 should be ignored, as if the parameter wasn't passed.
 def Test_prop_bufnr_zero()
   new

src/version.c

@@ -753,6 +753,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3706,
 /**/
     3705,
 /**/