[BUG]Cannot process correctly if file extension name is not lower case

[mikeshi80]

https://github.com/hymhub/pdf-vue3/blob/8249e9998e6ff2474d3e6af99ee3349d7edfbb8c/src/pdf-vue3.vue#L109

If the URL in the src ends with ".PDF" or ".Pdf", not all lower case characters, the URL will be recognised as base64 encoded data.