patch 8.2.0111: VAR_SPECIAL is also used for booleans

Problem:    VAR_SPECIAL is also used for booleans.
Solution:   Add VAR_BOOL for better type checking.
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 003d3b9..4465fc0 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -1067,7 +1067,7 @@
 {
     return ((argvars[0].v_type == VAR_NUMBER
 		&& argvars[0].vval.v_number != 0)
-	    || (argvars[0].v_type == VAR_SPECIAL
+	    || (argvars[0].v_type == VAR_BOOL
 		&& argvars[0].vval.v_number == VVAL_TRUE)
 	    || (argvars[0].v_type == VAR_STRING
 		&& argvars[0].vval.v_string != NULL
@@ -1811,6 +1811,7 @@
 	    n = argvars[0].vval.v_dict == NULL
 			|| argvars[0].vval.v_dict->dv_hashtab.ht_used == 0;
 	    break;
+	case VAR_BOOL:
 	case VAR_SPECIAL:
 	    n = argvars[0].vval.v_number != VVAL_TRUE;
 	    break;
@@ -4318,6 +4319,7 @@
 	    rettv->vval.v_number = dict_len(argvars[0].vval.v_dict);
 	    break;
 	case VAR_UNKNOWN:
+	case VAR_BOOL:
 	case VAR_SPECIAL:
 	case VAR_FLOAT:
 	case VAR_FUNC:
@@ -8341,20 +8343,15 @@
 
     switch (argvars[0].v_type)
     {
-	case VAR_NUMBER: n = VAR_TYPE_NUMBER; break;
-	case VAR_STRING: n = VAR_TYPE_STRING; break;
+	case VAR_NUMBER:  n = VAR_TYPE_NUMBER; break;
+	case VAR_STRING:  n = VAR_TYPE_STRING; break;
 	case VAR_PARTIAL:
-	case VAR_FUNC:   n = VAR_TYPE_FUNC; break;
-	case VAR_LIST:   n = VAR_TYPE_LIST; break;
-	case VAR_DICT:   n = VAR_TYPE_DICT; break;
-	case VAR_FLOAT:  n = VAR_TYPE_FLOAT; break;
-	case VAR_SPECIAL:
-	     if (argvars[0].vval.v_number == VVAL_FALSE
-		     || argvars[0].vval.v_number == VVAL_TRUE)
-		 n = VAR_TYPE_BOOL;
-	     else
-		 n = VAR_TYPE_NONE;
-	     break;
+	case VAR_FUNC:    n = VAR_TYPE_FUNC; break;
+	case VAR_LIST:    n = VAR_TYPE_LIST; break;
+	case VAR_DICT:    n = VAR_TYPE_DICT; break;
+	case VAR_FLOAT:   n = VAR_TYPE_FLOAT; break;
+	case VAR_BOOL:	  n = VAR_TYPE_BOOL; break;
+	case VAR_SPECIAL: n = VAR_TYPE_NONE; break;
 	case VAR_JOB:     n = VAR_TYPE_JOB; break;
 	case VAR_CHANNEL: n = VAR_TYPE_CHANNEL; break;
 	case VAR_BLOB:    n = VAR_TYPE_BLOB; break;