Fix double rotate behavior

Docs and warnings state that we ignore previous calls to `.rotate()` when multiple calls are made, but we were not correctly resetting the state at the start of the second call.

Author: happycollision

lib/operation.js

@@ -58,6 +58,8 @@ function rotate (angle, options) {
 
   if (this.options.angle || this.options.rotationAngle) {
     this.options.debuglog('ignoring previous rotate options');
+    this.options.angle = 0;
+    this.options.rotationAngle = 0;
   }
   if (is.integer(angle) && !(angle % 90)) {
     this.options.angle = angle;

test/unit/rotate.js

@@ -447,6 +447,30 @@ describe('Rotation', function () {
     assert.strictEqual(warningMessage, 'ignoring previous rotate options');
   });
 
+  it('Multiple rotate: last one wins (cardinal)', function (done) {
+    sharp(fixtures.inputJpg)
+      .rotate(45)
+      .rotate(90)
+      .toBuffer(function (err, data, info) {
+        if (err) throw err;
+        assert.strictEqual(2225, info.width);
+        assert.strictEqual(2725, info.height);
+        done();
+      });
+  });
+
+  it('Multiple rotate: last one wins (non cardinal)', function (done) {
+    sharp(fixtures.inputJpg)
+      .rotate(90)
+      .rotate(45)
+      .toBuffer(function (err, data, info) {
+        if (err) throw err;
+        assert.strictEqual(3500, info.width);
+        assert.strictEqual(3500, info.height);
+        done();
+      });
+  });
+
   it('Flip - vertical', function (done) {
     sharp(fixtures.inputJpg)
       .resize(320)