[MC-121714] Unable to save screenshots and world icons if the path contains non-ASCII characters

The bug

Taking a screenshot fails when the folder of your game profile contains non-ASCII characters.

18w06a

[22:40:50] [Client thread/WARN]: Couldn't save screenshot
java.io.IOException: Could not write image to the PNG file "###\screenshots\2018-02-11_22.40.50.png": Corrupt JPEG
	at csp.a(SourceFile:306) ~[18w06a.jar:?]
	at bxc.a(SourceFile:45) ~[18w06a.jar:?]
	at bxc.a(SourceFile:30) ~[18w06a.jar:?]
	at bwu.a(SourceFile:256) ~[18w06a.jar:?]
	at org.lwjgl.glfw.GLFWKeyCallbackI.callback(GLFWKeyCallbackI.java:23) [lwjgl-glfw-3.1.2.jar:?]
	at org.lwjgl.system.JNI.invokeV(Native Method) ~[lwjgl-3.1.2.jar:?]
	at org.lwjgl.glfw.GLFW.glfwPollEvents(GLFW.java:2520) [lwjgl-glfw-3.1.2.jar:?]
	at bwx.b(SourceFile:803) [18w06a.jar:?]
	at bwx.a(SourceFile:383) [18w06a.jar:?]
	at net.minecraft.client.main.Main.main(SourceFile:141) [18w06a.jar:?]

Additionally world icons cannot be saved either.

18w06a

[22:45:42] [Client thread/WARN]: Couldn't save auto screenshot
java.io.IOException: Could not write image to the PNG file "###\saves\New World\icon.png": Corrupt JPEG
	at csp.a(SourceFile:306) ~[18w06a.jar:?]
	at cjr.n(SourceFile:1039) [18w06a.jar:?]
	at cjr.a(SourceFile:949) [18w06a.jar:?]
	at bwx.b(SourceFile:823) [18w06a.jar:?]
	at bwx.a(SourceFile:383) [18w06a.jar:?]
	at net.minecraft.client.main.Main.main(SourceFile:141) [18w06a.jar:?]

Besides the profile name also having non-ascii chars in the world name triggers that issue:

18w20b

java.io.IOException: Could not write image to the PNG file "D:\mc\mn\bugs\.minecraft\saves\����BUG\icon.png": Corrupt JPEG
	at deq.a(SourceFile:306) ~[18w20b.jar:?]
	at cvd.o(SourceFile:870) [18w20b.jar:?]
	at cvd.a(SourceFile:783) [18w20b.jar:?]
	at cht.c(SourceFile:820) [18w20b.jar:?]
	at cht.a(SourceFile:381) [18w20b.jar:?]
	at net.minecraft.client.main.Main.main(SourceFile:144) [18w20b.jar:?]

How to reproduce

Create a folder whose name contains non-ASCII characters, for example the following
```
äö²³§ß
```
Launch Minecraft with this folder as game directory
Try to take a screenshot

Code analysis

Code analysis by [Mod] Pokechu22 can be found in this comment.