patch 8.2.1533: Vim9: error when passing getreginfo() result to setreg()

Problem:    Vim9: error when passing getreginfo() result to setreg().
Solution:   Use dict_get_bool() for "isunnamed". (closes #6784)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index fcfd4b1..270dcd2 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -7427,7 +7427,7 @@
 		regname = pointreg;
 	    }
 	}
-	else if (dict_get_number(d, (char_u *)"isunnamed"))
+	else if (dict_get_bool(d, (char_u *)"isunnamed", -1) > 0)
 	    pointreg = regname;
     }
     else