patch 8.0.0184: when an error is caught Vim still exits with non-zero result

Problem:    When in Ex mode and an error is caught by try-catch, Vim still
            exits with a non-zero exit code.
Solution:   Don't set ex_exitval when inside a try-catch. (partly by Christian
            Brabandt)

Author: brammool

src/message.c

@@ -578,8 +578,6 @@ emsg(char_u *s)
 	return TRUE;
 
     called_emsg = TRUE;
-    if (emsg_silent == 0)
-	ex_exitval = 1;
 
     /*
      * If "emsg_severe" is TRUE: When an error exception is to be thrown,
@@ -642,6 +640,8 @@ emsg(char_u *s)
 	    return TRUE;
 	}
 
+	ex_exitval = 1;
+
 	/* Reset msg_silent, an error causes messages to be switched back on. */
 	msg_silent = 0;
 	cmd_silent = FALSE;

src/testdir/test_system.vim

@@ -46,3 +46,40 @@ function! Test_System()
 
   call assert_fails('call system("wc -l", 99999)', 'E86:')
 endfunction
+
+function! Test_system_exmode()
+  let cmd=" -es -u NONE -c 'source Xscript' +q; echo $?"
+  " Need to put this in a script, "catch" isn't found after an unknown
+  " function.
+  call writefile(['try', 'call doesnotexist()', 'catch', 'endtry'], 'Xscript')
+  let a = system(v:progpath . cmd)
+  call assert_equal('0', a[0])
+  call assert_equal(0, v:shell_error)
+
+  " Error before try does set error flag.
+  call writefile(['call nosuchfunction()', 'try', 'call doesnotexist()', 'catch', 'endtry'], 'Xscript')
+  let a = system(v:progpath . cmd)
+  call assert_notequal('0', a[0])
+
+  let cmd=" -es -u NONE -c 'source Xscript' +q"
+  let a = system(v:progpath . cmd)
+  call assert_notequal(0, v:shell_error)
+
+  let cmd=" -es -u NONE -c 'call doesnotexist()' +q; echo $?"
+  let a = system(v:progpath. cmd)
+  call assert_notequal(0, a[0])
+
+  let cmd=" -es -u NONE -c 'call doesnotexist()' +q"
+  let a = system(v:progpath. cmd)
+  call assert_notequal(0, v:shell_error)
+
+  let cmd=" -es -u NONE -c 'call doesnotexist()|let a=1' +q; echo $?"
+  let a = system(v:progpath. cmd)
+  call assert_notequal(0, a[0])
+
+  let cmd=" -es -u NONE -c 'call doesnotexist()|let a=1' +q"
+  let a = system(v:progpath. cmd)
+  call assert_notequal(0, v:shell_error)
+
+  call delete('Xscript')
+endfunc

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    184,
 /**/
     183,
 /**/