Fix misuse of glTexImage2D.

Per the OpenGL documentation:
> GL_INVALID_VALUE may be generated if level is greater than
> log2(max), where max is the returned value of GL_MAX_TEXTURE_SIZE.

Although we always passed `log2(max) + 1` as `level`, for some reason
none of the GL implementations we run on ever returned an error.
It also appears there is a bug in ANGLE that crashes the process
instead in this case if the C++ runtime performs bound checks on
vector::operator[]=.

src/render/gl3shader.cpp

@@ -390,7 +390,7 @@ GLuint Generate(const std::vector<double> &pattern) {
     glGetIntegerv(GL_MAX_TEXTURE_SIZE, &size);
     RgbaColor *textureData = new RgbaColor[size];
 
-    int mipCount = (int)log2(size) + 1;
+    int mipCount = (int)log2(size);
     for(int mip = 0; mip < mipCount; mip++) {
         int dashI = 0;
         double dashT = 0.0;