fix(helpers): keep fullform singular for negative one-magnitude values

decorateResult() captured numericValue (used to pick the singular vs
plural fullform suffix) after the negative sign was already prefixed
onto result[0], so filesize(-1, {fullform: true}) compared -1 === 1
and wrongly pluralized to "-1 bytes" instead of "-1 byte". Capture the
magnitude before the sign is applied instead.

src/helpers.js

@@ -402,6 +402,16 @@ export function decorateResult(
 	bits,
 	roundingFunc,
 ) {
+	// Capture the number before the sign and the formatting: a comma decimal
+	// separator makes parseFloat read "1,5" as 1, and a leading "-" breaks the
+	// "=== 1" singular check.
+	let numericValue;
+	if (typeof result[0] === "string") {
+		numericValue = parseFloat(result[0]);
+	} else {
+		numericValue = result[0];
+	}
+
 	if (neg) {
 		// `precision` leaves the value as a string from toPrecision (e.g. "1.50").
 		// Negating that arithmetically coerces it back to a number and drops the
@@ -413,16 +423,6 @@ export function decorateResult(
 		result[1] = symbols[result[1]];
 	}
 
-	// Capture the numeric value before formatting; a comma decimal separator
-	// (via separator or a locale such as de-DE) would otherwise make parseFloat
-	// read "1,5" as 1 and select the singular unit name.
-	let numericValue;
-	if (typeof result[0] === "string") {
-		numericValue = parseFloat(result[0]);
-	} else {
-		numericValue = result[0];
-	}
-
 	result[0] = applyNumberFormatting(
 		result[0],
 		locale,