[cuebot] Fix for nullpointer jobs with str_loki_url set to null (#1713)

**Link the Issue(s) this Pull Request is related to.**
This is a fix for #1696 

**Summarize your change.**
Added a COALESCE in the dispatch database queries to make sure it
returns a valid string

Author: lithorus

cuebot/src/main/java/com/imageworks/spcue/dao/postgres/DispatchQuery.java

@@ -530,7 +530,7 @@ private static final String replaceQueryForFifo(String query) {
         "int_uid, " +
         "str_log_dir, " +
         "COALESCE(str_os, '') AS str_os, " +
-        "str_loki_url, " +
+        "COALESCE(str_loki_url, '') AS str_loki_url, " +
         "frame_name, " +
         "frame_state, " +
         "pk_frame, " +

cuebot/src/main/java/com/imageworks/spcue/dao/postgres/FrameDaoJdbc.java

@@ -245,10 +245,10 @@ public DispatchFrame mapRow(ResultSet rs, int rowNum) throws SQLException {
     private static final String GET_DISPATCH_FRAME = "SELECT " + "show.str_name AS show_name, "
             + "job.str_name AS job_name, " + "job.pk_job," + "job.pk_show," + "job.pk_facility,"
             + "job.str_name," + "job.str_shot," + "job.str_user," + "job.int_uid,"
-            + "job.str_log_dir," + "COALESCE(str_os, '') AS str_os, " + "job.str_loki_url, "
-            + "frame.str_name AS frame_name, " + "frame.str_state AS frame_state, "
-            + "frame.pk_frame, " + "frame.pk_layer, " + "frame.int_retries, "
-            + "frame.int_version, " + "layer.str_name AS layer_name, "
+            + "job.str_log_dir," + "COALESCE(str_os, '') AS str_os, "
+            + "COALESCE(str_loki_url, '') AS str_loki_url, " + "frame.str_name AS frame_name, "
+            + "frame.str_state AS frame_state, " + "frame.pk_frame, " + "frame.pk_layer, "
+            + "frame.int_retries, " + "frame.int_version, " + "layer.str_name AS layer_name, "
             + "layer.str_type AS layer_type, " + "layer.str_cmd, " + "layer.int_cores_min,"
             + "layer.int_cores_max," + "layer.b_threadable," + "layer.int_mem_min, "
             + "layer.int_gpus_min," + "layer.int_gpus_max," + "layer.int_gpu_mem_min, "