Fix handling of OpenGL resources

[DanRStevens]

It was recently noted that we might not be handling OpenGL resources correctly, such as by freeing them after we are done using them.

In Image.cpp in generateFbo there is a call to glGenTextures where the variable holding the ID simply goes out of scope. It does pass the value to glBindTexture first, but I doubt it get's read back and handled anywhere else.

The only potential use of the code in question is from RendererOpenGL::drawImageToImage, which is currently unused by NAS2D and OPHD.

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Relevant documentation:

• https://registry.khronos.org/OpenGL-Refpages/gl4/html/glGenBuffers.xhtml
• https://registry.khronos.org/OpenGL-Refpages/gl4/html/glDeleteBuffers.xhtml
• https://registry.khronos.org/OpenGL-Refpages/gl4/html/glGenTextures.xhtml
• https://registry.khronos.org/OpenGL-Refpages/gl4/html/glDeleteTextures.xhtml

Other related documentation:

• https://registry.khronos.org/OpenGL-Refpages/gl4/html/glBindBuffer.xhtml
• https://registry.khronos.org/OpenGL-Refpages/gl4/html/glBindTexture.xhtml
• https://registry.khronos.org/OpenGL-Refpages/gl2.1/xhtml/glVertexPointer.xml
• https://registry.khronos.org/OpenGL-Refpages/gl2.1/xhtml/glEnableClientState.xml
• https://registry.khronos.org/OpenGL-Refpages/gl2.1/xhtml/glEnableClientState.xml

Related:

• PR Fill texture coordinate array when initializing OpenGL #1227