Issue #148: Check for overflow when reading floating point exponent.

GCC with -O2 optimizes away the if(exp<-maxExponent) branch completely,
so we don't end up with the expected '512' value for overflowing
exponents. Limit the exponent parsing to MAX_INT instead to prevent
signed overflow from tripping up over-eager optimizing compilers.

jsdtoa.c

@@ -691,10 +691,12 @@ js_strtod(const char *string, char **endPtr)
 			}
 			expSign = FALSE;
 		}
-		while ((*p >= '0') && (*p <= '9')) {
+		while ((*p >= '0') && (*p <= '9') && exp < INT_MAX/10) {
 			exp = exp * 10 + (*p - '0');
 			p += 1;
 		}
+		while ((*p >= '0') && (*p <= '9'))
+			p += 1;
 	}
 	if (expSign) {
 		exp = fracExp - exp;