patch 8.1.1452: line and col property of popup windows not properly checked

Problem:    Line and col property of popup windows not properly checked.
Solution:   Check for "+" or "-" sign.
diff --git a/src/dict.c b/src/dict.c
index d6b3b18..c67eb42 100644
--- a/src/dict.c
+++ b/src/dict.c
@@ -605,6 +605,27 @@
 }
 
 /*
+ * Get a number item from a dictionary.
+ * Returns 0 if the entry doesn't exist.
+ * Give an error if the entry is not a number.
+ */
+    varnumber_T
+dict_get_number_check(dict_T *d, char_u *key)
+{
+    dictitem_T	*di;
+
+    di = dict_find(d, key, -1);
+    if (di == NULL)
+	return 0;
+    if (di->di_tv.v_type != VAR_NUMBER)
+    {
+	semsg(_(e_invarg2), tv_get_string(&di->di_tv));
+	return 0;
+    }
+    return tv_get_number(&di->di_tv);
+}
+
+/*
  * Return an allocated string with the string representation of a Dictionary.
  * May return NULL.
  */