improve sharing large images (#2020)

* log errors as such

* skip unneeded nil assignment

* prescale images to fit into extension restrictions

extensions must not use more than 120mb of memory,
this is easily exhausted by core scaling down images.

using iOS function for scaling use less memory (or the memory is not counted)
and avoids this error.

although we accept various formats of images,
in practise i've seen them passing to the extension only as URL,
if we see that for other formats as well, we can optimize the other branches,
currently, that seems not to be needed.

DcShare/Helper/ShareAttachment.swift

@@ -80,7 +80,7 @@ class ShareAttachment {
             case let url as URL:
                 result = SDAnimatedImage(contentsOfFile: url.path)
             default:
-                logger.debug("Unexpected data: \(type(of: data))")
+                logger.error("Unexpected data: \(type(of: data))")
             }
             if let result = result {
                 let path = ImageFormat.saveImage(image: result, directory: .cachesDirectory)
@@ -108,10 +108,12 @@ class ShareAttachment {
             case let data as Data:
                 result = ImageFormat.loadImageFrom(data: data)
             case let url as URL:
-                result = ImageFormat.loadImageFrom(url: url)
+                if let nsurl = NSURL(string: url.absoluteString) {
+                    // scaleDownImage() uses less memory than core and avoids exhausing the 120 mb memory restriction of extensions (see #1330)
+                    result = ImageFormat.scaleDownImage(nsurl, toMax: 1280)
+                }
             default:
-                logger.debug("Unexpected data: \(type(of: data))")
-                result = nil
+                logger.error("Unexpected data: \(type(of: data))")
             }
             if let result = result,
                let path = ImageFormat.saveImage(image: result, directory: .cachesDirectory) {
@@ -146,7 +148,7 @@ class ShareAttachment {
 
                 }
             default:
-                logger.debug("Unexpected data: \(type(of: data))")
+                logger.error("Unexpected data: \(type(of: data))")
             }
             if let error = error {
                 logger.error("Could not load share item as video: \(error.localizedDescription)")
@@ -182,7 +184,7 @@ class ShareAttachment {
                     self.generateThumbnailRepresentations(url: url)
                 }
             default:
-                logger.debug("Unexpected data: \(type(of: data))")
+                logger.error("Unexpected data: \(type(of: data))")
             }
             if let error = error {
                 logger.error("Could not load share item: \(error.localizedDescription)")
@@ -231,7 +233,7 @@ class ShareAttachment {
                 case let url as URL:
                     delegate.onUrlShared(url: url)
                 default:
-                    logger.debug("Unexpected data: \(type(of: data))")
+                    logger.error("Unexpected data: \(type(of: data))")
                 }
                 if let error = error {
                     logger.error("Could not share URL: \(error.localizedDescription)")