Fix documented errors for gamma ramp functions

Fixes #2186

CONTRIBUTORS.md

@@ -33,6 +33,7 @@ video tutorials.
  - Arturo Castro
  - Chi-kwan Chan
  - TheChocolateOre
+ - Ali Chraghi
  - Joseph Chua
  - Ian Clarkson
  - Michał Cichoń

include/GLFW/glfw3.h

@@ -2835,11 +2835,11 @@ GLFWAPI const GLFWvidmode* glfwGetVideoMode(GLFWmonitor* monitor);
  *  @param[in] monitor The monitor whose gamma ramp to set.
  *  @param[in] gamma The desired exponent.
  *
- *  @errors Possible errors include @ref GLFW_NOT_INITIALIZED, @ref
+ *  @errors Possible errors include @ref GLFW_NOT_INITIALIZED, @ref GLFW_INVALID_VALUE,
- *  GLFW_INVALID_VALUE and @ref GLFW_PLATFORM_ERROR.
+ *  @ref GLFW_PLATFORM_ERROR and @ref GLFW_FEATURE_UNAVAILABLE (see remarks).
  *
  *  @remark @wayland Gamma handling is a privileged protocol, this function
- *  will thus never be implemented and emits @ref GLFW_PLATFORM_ERROR.
+ *  will thus never be implemented and emits @ref GLFW_FEATURE_UNAVAILABLE.
  *
  *  @thread_safety This function must only be called from the main thread.
  *
@@ -2859,11 +2859,11 @@ GLFWAPI void glfwSetGamma(GLFWmonitor* monitor, float gamma);
  *  @return The current gamma ramp, or `NULL` if an
  *  [error](@ref error_handling) occurred.
  *
- *  @errors Possible errors include @ref GLFW_NOT_INITIALIZED and @ref
+ *  @errors Possible errors include @ref GLFW_NOT_INITIALIZED, @ref GLFW_PLATFORM_ERROR
- *  GLFW_PLATFORM_ERROR.
+ *  and @ref GLFW_FEATURE_UNAVAILABLE (see remarks).
  *
  *  @remark @wayland Gamma handling is a privileged protocol, this function
- *  will thus never be implemented and emits @ref GLFW_PLATFORM_ERROR while
+ *  will thus never be implemented and emits @ref GLFW_FEATURE_UNAVAILABLE while
  *  returning `NULL`.
  *
  *  @pointer_lifetime The returned structure and its arrays are allocated and
@@ -2898,8 +2898,8 @@ GLFWAPI const GLFWgammaramp* glfwGetGammaRamp(GLFWmonitor* monitor);
  *  @param[in] monitor The monitor whose gamma ramp to set.
  *  @param[in] ramp The gamma ramp to use.
  *
- *  @errors Possible errors include @ref GLFW_NOT_INITIALIZED and @ref
+ *  @errors Possible errors include @ref GLFW_NOT_INITIALIZED, @ref GLFW_PLATFORM_ERROR
- *  GLFW_PLATFORM_ERROR.
+ *  and @ref GLFW_FEATURE_UNAVAILABLE (see remarks).
  *
  *  @remark The size of the specified gamma ramp should match the size of the
  *  current ramp for that monitor.
@@ -2907,7 +2907,7 @@ GLFWAPI const GLFWgammaramp* glfwGetGammaRamp(GLFWmonitor* monitor);
  *  @remark @win32 The gamma ramp size must be 256.
  *
  *  @remark @wayland Gamma handling is a privileged protocol, this function
- *  will thus never be implemented and emits @ref GLFW_PLATFORM_ERROR.
+ *  will thus never be implemented and emits @ref GLFW_FEATURE_UNAVAILABLE.
  *
  *  @pointer_lifetime The specified gamma ramp is copied before this function
  *  returns.