Skip leading whitespace in Q_atoi and Q_atof

This matches the standard library and also fixes the following bug:
- load ad_sepulcher and move to an area where water is visible
- open up the console
- save waterbug
- load waterbug
Water is now invisible as long as the console is still active.

The issue stems from the fact that cvar_set is called at startup
with the arguments ("r_wateralpha", ftos(liquid_alpha)) [1],
and ftos pads its output ("  0.6"). Without skipping the leading
whitespace, Q_atof ends up returning 0, which then gets assigned
to r_wateralpha. This makes the water invisible until a stuffcmd
that sets r_wateralpha again is later received from the server.
With the console open at startup, however, the stuffcmd message
can be delayed indefinitely.

[1] 320f1cec45/world.qc (L641)

Quake/common.c

@@ -421,6 +421,9 @@ int Q_atoi (const char *str)
 	int		sign;
 	int		c;
 
+	while (q_isspace (*str))
+		++str;
+
 	if (*str == '-')
 	{
 		sign = -1;
@@ -481,6 +484,9 @@ float Q_atof (const char *str)
 	int		c;
 	int	decimal, total;
 
+	while (q_isspace (*str))
+		++str;
+
 	if (*str == '-')
 	{
 		sign = -1;