libobs: Disallow overwriting the crash handler

Setting a new crash handler overwrites the existing one. This is not
desirable.

Author: gxalpha

docs/sphinx/reference-libobs-util-base.rst

@@ -55,6 +55,7 @@ Logging Functions
 .. function:: void base_set_crash_handler(void (*handler)(const char *, va_list, void *), void *param)
 
    Sets the current crash handler.
+   This may only be set once.
 
 ---------------------
 

libobs/util/base.c

@@ -83,6 +83,12 @@ void base_set_log_handler(log_handler_t handler, void *param)
 
 void base_set_crash_handler(void (*handler)(const char *, va_list, void *), void *param)
 {
+	if (crash_handler || crash_param) {
+		blog(LOG_ERROR, "Tried to set a crash handler when one already exists."
+				"This is unsupported, and will crash in a future version of OBS.");
+		return;
+	}
+
 	crash_param = param;
 	crash_handler = handler;
 }