Handle nested textual tags

This bug was also catched by regression tests. Single state was
overriden in opentag/closetag callbacks. Using stack state solved the
problem with nested textual tags.

Now many whitespaces bugs should go away.

lib/svgo/svg2js.js

@@ -26,8 +26,7 @@ module.exports = function(data) {
     var sax = SAX.parser(config.strict, config),
         root = new JSAPI({ elem: '#document', content: [] }),
         current = root,
-        stack = [root],
-        textContext = null;
+        stack = [root];
 
     function pushToContent(content) {
 
@@ -116,39 +115,22 @@ module.exports = function(data) {
         elem = pushToContent(elem);
         current = elem;
 
-        // Save info about tags containing text to prevent trimming of meaningful whitespace
-        if (textElems.includes(data.name) && !data.prefix) {
-            textContext = current;
-        }
-
         stack.push(elem);
 
     };
 
     sax.ontext = function(text) {
-
-        if (/\S/.test(text) || textContext) {
-
-            if (!textContext)
-                text = text.trim();
-
-            pushToContent({
-                text: text
-            });
-
-        }
-
+      // prevent trimming of meaningful whitespace inside textual tags
+      if (textElems.includes(current.elem) && !data.prefix) {
+        pushToContent({ text: text });
+      } else if (/\S/.test(text)) {
+        pushToContent({ text: text.trim() });
+      }
     };
 
     sax.onclosetag = function() {
-
-        var last = stack.pop();
-
-        if (last == textContext) {
-            textContext = null;
-        }
-        current = stack[stack.length - 1];
-
+      stack.pop();
+      current = stack[stack.length - 1];
     };
 
     sax.onerror = function(e) {

test/svgo/_index.js

@@ -71,4 +71,9 @@ describe('svgo', () => {
     const result = optimize(original, { path: 'input.svg', plugins: [], js2svg: { pretty: true } });
     expect(normalize(result.data)).to.equal(expected);
   });
+  it('should preserve whitespaces between tspan tags', async () => {
+    const [original, expected] = await parseFixture('whitespaces.svg');
+    const result = optimize(original, { path: 'input.svg', js2svg: { pretty: true } });
+    expect(normalize(result.data)).to.equal(expected);
+  });
 });