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/if_mzsch.c b/src/if_mzsch.c
index bf0157a..e31d0e1 100644
--- a/src/if_mzsch.c
+++ b/src/if_mzsch.c
@@ -3136,7 +3136,7 @@
 	    MZ_GC_UNREG();
 	}
     }
-    else if (vim_value->v_type == VAR_SPECIAL)
+    else if (vim_value->v_type == VAR_BOOL || vim_value->v_type == VAR_SPECIAL)
     {
 	if (vim_value->vval.v_number <= VVAL_TRUE)
 	    result = scheme_make_integer((long)vim_value->vval.v_number);
@@ -3218,7 +3218,7 @@
     }
     else if (SCHEME_BOOLP(obj))
     {
-	tv->v_type = VAR_SPECIAL;
+	tv->v_type = VAR_BOOL;
 	tv->vval.v_number = SCHEME_TRUEP(obj);
     }
 # ifdef FEAT_FLOAT