Ensure trim is no-op when it would reduce to nothing #3223

lib/resize.js

@@ -433,6 +433,8 @@ function extract (options) {
  *
  * Images with an alpha channel will use the combined bounding box of alpha and non-alpha channels.
  *
+ * If the result of this operation would trim an image to nothing then no change is made.
+ *
  * The `info` response Object, obtained from callback of `.toFile()` or `.toBuffer()`,
  * will contain `trimOffsetLeft` and `trimOffsetTop` properties.
  *