fix regression in cover fetching (#5621)
introduced in https://github.com/tachiyomiorg/tachiyomi/pull/4870
this was previously done here: https://github.com/tachiyomiorg/tachiyomi/blob/7d23fd8ef5bbb9efd12f65bb5c9670464dd6c0b1/app/src/main/java/eu/kanade/tachiyomi/data/glide/MangaThumbnailModelLoader.kt#L95 as part of https://github.com/tachiyomiorg/tachiyomi/pull/2908
this impacts Komga extension, where server url is manually provided by the user, but due to auto-correct on mobile keyboards the `http` prefix sometimes get capitalized to `Http`.