Fix memory leak related to STBImage

[MESLewis]

[LWJGL] 1048577 bytes leaked, thread 1 (main), address: 0x136D54C1040
	at org.lwjgl.stb.STBImage.nstbi_load_from_memory(Native Method)
	at org.lwjgl.stb.STBImage.stbi_load_from_memory(STBImage.java:259)
	at org.lwjglx.debug.$Proxy$655.stbi_load_from_memory43(Unknown Source)
	at com.meslewis.simplegltf2.simpleviewer.render.RenderTexture.loadData(RenderTexture.java:92)
	at com.meslewis.simplegltf2.simpleviewer.GlUtil.loadImageToTexture(GlUtil.java:204)
	at com.meslewis.simplegltf2.simpleviewer.GlUtil.setTexture(GlUtil.java:186)
	at com.meslewis.simplegltf2.simpleviewer.GlUtil.setTexture(GlUtil.java:157)
	at com.meslewis.simplegltf2.simpleviewer.render.Renderer.drawRenderObject(Renderer.java:315)
	at com.meslewis.simplegltf2.simpleviewer.render.Renderer.draw(Renderer.java:162)
	at com.meslewis.simplegltf2.simpleviewer.render.Renderer.draw(Renderer.java:172)
	at com.meslewis.simplegltf2.simpleviewer.render.Renderer.draw(Renderer.java:172)
	at com.meslewis.simplegltf2.simpleviewer.render.Renderer.draw(Renderer.java:172)
	at com.meslewis.simplegltf2.simpleviewer.render.Renderer.draw(Renderer.java:172)
	at com.meslewis.simplegltf2.simpleviewer.render.Renderer.draw(Renderer.java:172)
	at com.meslewis.simplegltf2.simpleviewer.render.Renderer.draw(Renderer.java:141)
	at com.meslewis.simplegltf2.simpleviewer.SimpleViewer.loop(SimpleViewer.java:397)
	at com.meslewis.simplegltf2.simpleviewer.SimpleViewer.run(SimpleViewer.java:163)
	at com.meslewis.simplegltf2.simpleviewer.SimpleViewer.main(SimpleViewer.java:528)