Fix printf funcs on memory pressure with floats (#1275)

Cosmopolitan's printf-family functions will currently crash if one tries
formatting a floating point number with a larger precision (large enough
that gdtoa attempts to allocate memory to format the number) while under
memory pressure (i.e. when malloc fails) because gdtoa fails to check if
malloc fails.

The added tests (which would previously crash under cosmopolitan without
this patch) show how to reproduce the issue.

This patch fixes this, and adds the aforementioned tests.

third_party/gdtoa/dmisc.c

@@ -49,6 +49,8 @@ __gdtoa_rv_alloc(int i, ThInfo **PTI)
 	     j <<= 1)
 		k++;
 	r = (int *)__gdtoa_Balloc(k, PTI);
+	if (r == NULL)
+		return NULL;
 	*r = k;
 	return (char *)(r + 1);
 }

third_party/gdtoa/dtoa.c

@@ -246,6 +246,9 @@ dtoa(double d0, int mode, int ndigits, int *decpt, int *sign, char **rve)
 			i = 1;
 	}
 	s = s0 = __gdtoa_rv_alloc(i, &TI);
+	if (s0 == NULL)
+		goto ret1;
+
 	if (mode > 1 && Rounding != 1)
 		leftright = 0;
 	if (ilim >= 0 && ilim <= Quick_max && try_quick) {
@@ -614,7 +617,8 @@ retc:
 		--s;
 ret1:
 	__gdtoa_Bfree(b, &TI);
-	*s = 0;
+	if (s != NULL)
+		*s = 0;
 	*decpt = k + 1;
 	if (rve)
 		*rve = s;

third_party/gdtoa/gdtoa.c

@@ -286,6 +286,8 @@ gdtoa(const FPI *fpi, int be, ULong *bits, int *kindp, int mode, int ndigits, in
 			i = 1;
 	}
 	s = s0 = __gdtoa_rv_alloc(i, &TI);
+	if (s0 == NULL)
+		goto ret1;
 	if (mode <= 1)
 		rdir = 0;
 	else if ( (rdir = fpi->rounding - 1) !=0) {
@@ -673,10 +675,12 @@ ret:
 		__gdtoa_Bfree(mhi, &TI);
 	}
 ret1:
-	while(s > s0 && s[-1] == '0')
-		--s;
+	if (s != NULL)
+		while(s > s0 && s[-1] == '0')
+			--s;
 	__gdtoa_Bfree(b, &TI);
-	*s = 0;
+	if (s != NULL)
+		*s = 0;
 	*decpt = k + 1;
 	if (rve)
 		*rve = s;

third_party/gdtoa/misc.c

@@ -129,12 +129,16 @@ __gdtoa_Balloc(int k, ThInfo **PTI)
 	} else {
 		x = 1 << k;
 		rv = malloc(sizeof(Bigint) + (x-1)*sizeof(ULong));
+		if (rv == NULL)
+			goto ret;
 		rv->k = k;
 		rv->maxwds = x;
 	}
+	rv->sign = rv->wds = 0;
+
+ret:
 	if (TI == &TI0)
 		__gdtoa_unlock();
-	rv->sign = rv->wds = 0;
 	return rv;
 }