patch 8.2.1603: Vim9: cannot use "true" with getchar()

Problem:    Vim9: cannot use "true" with getchar().
Solution:   use tv_get_bool_chk(). (closes #6874)

Author: brammool

src/getchar.c

@@ -2037,7 +2037,7 @@ f_getchar(typval_T *argvars, typval_T *rettv)
 	if (argvars[0].v_type == VAR_UNKNOWN)
 	    // getchar(): blocking wait.
 	    n = plain_vgetc();
-	else if (tv_get_number_chk(&argvars[0], &error) == 1)
+	else if (tv_get_bool_chk(&argvars[0], &error))
 	    // getchar(1): only check if char avail
 	    n = vpeekc_any();
 	else if (error || vpeekc_any() == NUL)

src/testdir/test_vim9_func.vim

@@ -1505,6 +1505,10 @@ def Test_getbufinfo()
   bwipe Xtestfile1 Xtestfile2
 enddef
 
+def Test_getchar()
+  assert_equal(0, getchar(true))
+enddef
+
 def Fibonacci(n: number): number
   if n < 2
     return n

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1603,
 /**/
     1602,
 /**/