fix issue when image not saved after attaching (#8957)

diff --git a/erpnext/crm/doctype/lead/lead.py b/erpnext/crm/doctype/lead/lead.py
index e6659f3..ccbb536 100644
--- a/erpnext/crm/doctype/lead/lead.py
+++ b/erpnext/crm/doctype/lead/lead.py
@@ -43,7 +43,8 @@
 			if self.email_id == self.contact_by:
 				frappe.throw(_("Next Contact By cannot be same as the Lead Email Address"))
 
-			self.image = has_gravatar(self.email_id)
+			if self.is_new() or not self.image:
+				self.image = has_gravatar(self.email_id)
 
 		if self.contact_date and self.contact_date < now():
 			frappe.throw(_("Next Contact Date cannot be in the past"))