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OpenGL: Clamp textures

This fixes this weird thing you'd see in the enhanced branch if the
screen is scaled (happens if you resize the window).

When the screen is scaled, OpenGL uses linear interpolation. This
would cause it to fetch samples from outside the texture. IIRC, by
default, the default behaviour is GL_REPEAT, which causes it to blend
with samples from the other side of the texture, creating strange
pixels at the end of the screen.

--- a/src/Backends/Rendering/OpenGL3.cpp

+++ b/src/Backends/Rendering/OpenGL3.cpp

@@ -242,6 +242,9 @@

 	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB8, window_width, window_height, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);

 	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

 	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);

+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);

 	framebuffer_surface.width = window_width;

 	framebuffer_surface.height = window_height;

@@ -318,6 +321,9 @@

 	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB8, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);

 	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

 	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);

+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);

 	surface->width = width;

 	surface->height = height;

@@ -528,6 +534,9 @@

 	glTexImage2D(GL_TEXTURE_2D, 0, GL_R8, width, height, 0,  GL_RED, GL_UNSIGNED_BYTE, buffer);

 	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

 	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);

+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);

 	glyph->width = width;

 	glyph->height = height;