fix(DistanceMatrix): fromCompact with an empty array

It was creating a distance matrix
with `1` as `diagonalSize` instead `0`

src/__tests__/distance_matrix/creation.test.js

@@ -83,6 +83,10 @@ describe('DistanceMatrix creation', () => {
     );
   });
 
+  it('fromCompact empty', () => {
+    expect(DistanceMatrix.fromCompact([]).to2DArray()).toStrictEqual([]);
+  });
+
   it('zeros', () => {
     expect(DistanceMatrix.zeros(3).to2DArray()).toStrictEqual([
       [0, 0, 0],

src/__tests__/distance_matrix/export.test.js

@@ -13,6 +13,10 @@ describe('DistanceMatrix export', () => {
     expect(matrix.toCompact()).toStrictEqual([1, 2, 3, 2, 3, 3]);
   });
 
+  it('toCompact empty', () => {
+    expect(new DistanceMatrix(0).toCompact()).toStrictEqual([]);
+  });
+
   it('toSymmetricMatrix', () => {
     const matrix = new DistanceMatrix([
       [0, 1, 2, 3],

src/distanceMatrix.js

@@ -97,6 +97,12 @@ export class DistanceMatrix extends SymmetricMatrix {
    */
   static fromCompact(compact) {
     const compactSize = compact.length;
+
+    if (compactSize === 0) {
+      return new this(0);
+    }
+
+    // compactSize in Natural integer range ]0;∞]
     // compactSize = (sideSize * (sideSize - 1)) / 2
     // sideSize = (Sqrt(8 × compactSize + 1) + 1) / 2
     const diagonalSize = (Math.sqrt(8 * compactSize + 1) + 1) / 2;