[Fix] Core: Fix processing of NDNs of certain type

src/libmime/mime_parser.c

 						FALSE);
 			}
 		}
+		else {
+			body_pos = 0;
+
+			hdrs = rspamd_message_get_header_from_hash (npart->raw_headers,
+					task->task_pool,
+					"Content-Type", FALSE);
+		}
 
 		pbegin = part->parsed_data.begin + body_pos;
 		plen = part->parsed_data.len - body_pos;
-
-		hdrs = rspamd_message_get_header_from_hash (npart->raw_headers,
-				task->task_pool,
-				"Content-Type", FALSE);
 	}
 
 	npart->raw_data.begin = pbegin;