Initialize all idRegister class members in constructors

in SkinDeep regs not being initialized caused random crashes
(in dhewm3 I haven't seen that so far, but fixing this won't hurt).

From SkinDeep commit message:

In idRegister::SetToRegs() at `registers[ regs[ i ] ] = v[i];`
regs[i] contained values like 21845 or 22010 or 32272, even though
the static registers array that's written to there only holds 4096
elements (it's `static float regs[MAX_EXPRESSION_REGISTERS];`
 from `idWindow::EvalRegs()`).
So it overwrites other data, likely other global variables, like
`gameLocal.entities[4967]`, that now contain garbage and next time
someone tries to use them, bad things happen.
In this case, if someone tries to dereference gameLocal.entities[i]
and the pointer at i contains garbage, there's a segfault (crash).

DanielGibson/SkinDeep@462404a

Author: DanielGibson

neo/ui/RegExp.h

@@ -58,13 +58,19 @@ class idRegister {
 };
 
 ID_INLINE idRegister::idRegister( void ) {
+	enabled = false;
+	type = -1;
+	regCount = 0;
+	memset(regs, 0, sizeof(regs));
+	var = NULL;
 }
 
 ID_INLINE idRegister::idRegister( const char *p, int t ) {
 	name = p;
 	type = t;
 	assert( t >= 0 && t < NUMTYPES );
 	regCount = REGCOUNT[t];
+	memset(regs, 0, sizeof(regs));
 	enabled = ( type == STRING ) ? false : true;
 	var = NULL;
 };