Handle images without width/height info correctly

Prior to #1912, height fix up of image events without an `info` in their
content would fail, setting `style.height = null + "px"`.

Now that all thumbnail sizing is done through one path, we can fix the
same problem for all cases (images, stickers, e2e/non-e2e) by handling
images without `info` correctly.

At the bare minimum, we use a null-guard that will make sure an image
without an `info` does not appear in the timeline (as a spinner or
otherwise until loaded). When loaded, we size it like any other image
by using the natural dimensions of the loaded image in place of `info`.

Note that we do not apply the same logic to images that *do* specify an
`info` with `w` and `h` keys. If the aspect ratio of the image does not
match that of the event, we use the one in `info` even when the image
has loaded.

src/components/views/messages/MImageBody.js

@@ -147,7 +147,16 @@ export default class extends React.Component {
 
     onImageLoad() {
         this.props.onWidgetLoad();
-        this.setState({ imgLoaded: true });
+
+        let loadedImageDimensions;
+
+        if (this.refs.image) {
+            const { naturalWidth, naturalHeight } = this.refs.image;
+
+            loadedImageDimensions = { naturalWidth, naturalHeight };
+        }
+
+        this.setState({ imgLoaded: true, loadedImageDimensions });
     }
 
     _getContentUrl() {
@@ -239,13 +248,30 @@ export default class extends React.Component {
     }
 
     _messageContent(contentUrl, thumbUrl, content) {
-        // If unspecifide in the thumbnail info, assume width x height to be 800 x 600.
+        let infoWidth;
-        let infoHeight = 600;
+        let infoHeight;
-        let infoWidth = 800;
 
-        if (content.info && content.info.h && content.info.w) {
+        if (content && content.info && content.info.w && content.info.h) {
-            infoHeight = content.info.h;
             infoWidth = content.info.w;
+            infoHeight = content.info.h;
+        } else {
+            // Whilst the image loads, display nothing.
+            //
+            // Once loaded, use the loaded image dimensions stored in `loadedImageDimensions`.
+            //
+            // By doing this, the image "pops" into the timeline, but is still restricted
+            // by the same width and height logic below.
+            if (!this.state.loadedImageDimensions) {
+                return this.wrapImage(contentUrl,
+                    <img style={{display: 'none'}} src={thumbUrl} ref="image"
+                        alt={content.body}
+                        onError={this.onImageError}
+                        onLoad={this.onImageLoad}
+                    />,
+                );
+            }
+            infoWidth = this.state.loadedImageDimensions.naturalWidth;
+            infoHeight = this.state.loadedImageDimensions.naturalHeight;
         }
 
         // The maximum height of the thumbnail as it is rendered as an <img>