A bunch of fixes for Pose Library while checking on T51607

* Display a warning above the pose list if the pose library is in an invalid
  state (i.e. when it has keyframes but no pose-markers associated with those
  keyframes). This warning prompts users to run the "Sanitize Pose Library Action"
  operator, which should fix up such issues.

* "Sanitize" operator now creates unique names for each newly create pose
  marker it generates, including the frame on which it found the pose

release/scripts/startup/bl_ui/properties_data_armature.py

@@ -178,6 +178,10 @@ class DATA_PT_pose_library(ArmatureButtonsPanel, Panel):
         layout.template_ID(ob, "pose_library", new="poselib.new", unlink="poselib.unlink")
 
         if poselib:
+            # warning about poselib being in an invalid state
+            if len(poselib.fcurves) > 0 and len(poselib.pose_markers) == 0:
+                layout.label(icon='ERROR', text="Error: Potentially corrupt library, run 'Sanitize' operator to fix") 
+
             # list of poses in pose library
             row = layout.row()
             row.template_list("UI_UL_list", "pose_markers", poselib, "pose_markers",

source/blender/editors/armature/pose_lib.c

@@ -328,7 +328,7 @@ static int poselib_sanitize_exec(bContext *C, wmOperator *op)
 			/* add pose to poselib */
 			marker = MEM_callocN(sizeof(TimeMarker), "ActionMarker");
 			
-			BLI_strncpy(marker->name, "Pose", sizeof(marker->name));
+			BLI_snprintf(marker->name, sizeof(marker->name), "F%d Pose", (int)ak->cfra);
 			
 			marker->frame = (int)ak->cfra;
 			marker->flag = -1;