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/json.c b/src/json.c
index eedb606..64ef93f 100644
--- a/src/json.c
+++ b/src/json.c
@@ -193,11 +193,17 @@
 
     switch (val->v_type)
     {
-	case VAR_SPECIAL:
+	case VAR_BOOL:
 	    switch (val->vval.v_number)
 	    {
 		case VVAL_FALSE: ga_concat(gap, (char_u *)"false"); break;
 		case VVAL_TRUE: ga_concat(gap, (char_u *)"true"); break;
+	    }
+	    break;
+
+	case VAR_SPECIAL:
+	    switch (val->vval.v_number)
+	    {
 		case VVAL_NONE: if ((options & JSON_JS) != 0
 					     && (options & JSON_NO_NONE) == 0)
 				    // empty item
@@ -818,7 +824,7 @@
 			reader->js_used += 5;
 			if (cur_item != NULL)
 			{
-			    cur_item->v_type = VAR_SPECIAL;
+			    cur_item->v_type = VAR_BOOL;
 			    cur_item->vval.v_number = VVAL_FALSE;
 			}
 			retval = OK;
@@ -829,7 +835,7 @@
 			reader->js_used += 4;
 			if (cur_item != NULL)
 			{
-			    cur_item->v_type = VAR_SPECIAL;
+			    cur_item->v_type = VAR_BOOL;
 			    cur_item->vval.v_number = VVAL_TRUE;
 			}
 			retval = OK;