chore: mention deletion of reference in endpoint documentation

Controllers/UserContentController.cs

@@ -154,9 +154,13 @@ public class UserContentController : ControllerBase
     /// [AUTHED] Delete an image
     /// </summary>
     /// <remarks>
-    /// Deletes an image, granted it exists. <br/>
+    /// Deletes an image, granted it exists.
+    /// <br/><br/>
     /// <b>Note</b>:
-    /// If the image is a file on disk, it's also deleted.
+    /// If the image is a file on disk, it's also deleted. 
+    /// <br/><br/>
+    /// <b>Warning</b>:
+    /// Any reference to deleted image in Quotes table will also be deleted (nullified).
     /// </remarks>
     /// <returns>Json with status</returns>
     /// <param name="id">Image id which will be deleted</param>
@@ -189,6 +193,18 @@ public class UserContentController : ControllerBase
         }
 
         // - from db
+        //    - first, from any quotes that reference it
+        List<Quote> quotesToModify = await _db.Quotes
+                                            .Include(q => q.Image)
+                                            .Where(q => q.Image == image)
+                                            .ToListAsync();
+
+        foreach (Quote quote in quotesToModify)
+        {
+            quote.Image = null;
+        }
+
+        //    - finally, from images table
         _db.Images.Remove(image);
         await _db.SaveChangesAsync();