Add an explicit fflush() when writing the config.

Yes, fclose() flushes the stream and yes, this is unnecessary. But I've
seen at least two times partial written configs on Win 10. :(

src/client/cl_main.c

@@ -639,6 +639,8 @@ CL_WriteConfiguration(void)
 	fprintf(f, "// generated by quake, do not modify\n");
 
 	Key_WriteBindings(f);
+
+	fflush(f);
 	fclose(f);
 
 	Cvar_WriteVariables(path);

src/common/cvar.c

@@ -471,6 +471,7 @@ Cvar_WriteVariables(char *path)
 		}
 	}
 
+	fflush(f);
 	fclose(f);
 }