fix(loaders): properly catches render errors and calls onError callback

related issue: #16

the problem is caused by the fact that an empty string or any other "real-file-but-not-an-image" (an empty string is a request to load index.html basically) gets fulfilled by the server with a 200 OK status, returned by FileLoader -> we get the HTML in return (which is not an image) and then we try to render it anyway.

this catches errors in the LoaderBase render function and properly calls the onError callback

src/decode/loaders/GainMapLoader.ts

@@ -79,7 +79,17 @@ export class GainMapLoader extends LoaderBase<[string, string, string]> {
 
     const loadCheck = async () => {
       if (sdr && gainMap && metadata) {
-        await this.render(quadRenderer, metadata, sdr, gainMap)
+        // solves #16
+        try {
+          await this.render(quadRenderer, metadata, sdr, gainMap)
+        } catch (error) {
+          this.manager.itemError(sdrUrl)
+          this.manager.itemError(gainMapUrl)
+          this.manager.itemError(metadataUrl)
+          if (typeof onError === 'function') onError(error)
+          quadRenderer.disposeOnDemandRenderer()
+          return
+        }
 
         if (typeof onLoad === 'function') onLoad(quadRenderer)
         this.manager.itemEnd(sdrUrl)

src/decode/loaders/HDRJPGLoader.ts

@@ -109,7 +109,16 @@ export class HDRJPGLoader extends LoaderBase<string> {
           throw e
         }
       }
-      await this.render(quadRenderer, metadata, sdrJPEG, gainMapJPEG)
+
+      // solves #16
+      try {
+        await this.render(quadRenderer, metadata, sdrJPEG, gainMapJPEG)
+      } catch (error) {
+        this.manager.itemError(url)
+        if (typeof onError === 'function') onError(error)
+        quadRenderer.disposeOnDemandRenderer()
+        return
+      }
 
       if (typeof onLoad === 'function') onLoad(quadRenderer)
       this.manager.itemEnd(url)