fix make-variables library bug

by checking for empty-string name.

libraries/make-variables.xml

@@ -1 +1 @@
-<blocks app="Snap! 4.1, http://snap.berkeley.edu" version="1"><block-definition s="global variables %&apos;names&apos;" type="command" category="variables"><header></header><code></code><translations></translations><inputs><input type="%mult%txt"></input></inputs><script><block s="doForEach"><l>each item</l><block var="names"/><script><block s="doRun"><block s="reportJSFunction"><list><l>name</l></list><l>this.addVariable(name, true);</l></block><list><block var="each item"/></list></block></script></block><block s="doRun"><block s="reportJSFunction"><list></list><l>var ide = this.parentThatIsA(IDE_Morph);&#xD;ide.flushBlocksCache(&apos;variables&apos;); // b/c of inheritance&#xD;ide.refreshPalette();</l></block><list></list></block></script></block-definition><block-definition s="sprite-local variables %&apos;names&apos;" type="command" category="variables"><header></header><code></code><translations></translations><inputs><input type="%mult%txt"></input></inputs><script><block s="doForEach"><l>each item</l><block var="names"/><script><block s="doRun"><block s="reportJSFunction"><list><l>name</l></list><l>this.addVariable(name, false);</l></block><list><block var="each item"/></list></block></script></block><block s="doRun"><block s="reportJSFunction"><list></list><l>var ide = this.parentThatIsA(IDE_Morph);&#xD;ide.flushBlocksCache(&apos;variables&apos;); // b/c of inheritance&#xD;ide.refreshPalette();</l></block><list></list></block></script></block-definition></blocks>
+<blocks app="Snap! 4.1, http://snap.berkeley.edu" version="1"><block-definition s="global variables %&apos;names&apos;" type="command" category="variables"><header></header><code></code><translations></translations><inputs><input type="%mult%txt"></input></inputs><script><block s="doForEach"><l>each item</l><block var="names"/><script><block s="doRun"><block s="reportJSFunction"><list><l>name</l></list><l>if (name != "") this.addVariable(name, true);</l></block><list><block var="each item"/></list></block></script></block><block s="doRun"><block s="reportJSFunction"><list></list><l>var ide = this.parentThatIsA(IDE_Morph);&#xD;ide.flushBlocksCache(&apos;variables&apos;); // b/c of inheritance&#xD;ide.refreshPalette();</l></block><list></list></block></script></block-definition><block-definition s="sprite-local variables %&apos;names&apos;" type="command" category="variables"><header></header><code></code><translations></translations><inputs><input type="%mult%txt"></input></inputs><script><block s="doForEach"><l>each item</l><block var="names"/><script><block s="doRun"><block s="reportJSFunction"><list><l>name</l></list><l>if (name != "") this.addVariable(name, false);</l></block><list><block var="each item"/></list></block></script></block><block s="doRun"><block s="reportJSFunction"><list></list><l>var ide = this.parentThatIsA(IDE_Morph);&#xD;ide.flushBlocksCache(&apos;variables&apos;); // b/c of inheritance&#xD;ide.refreshPalette();</l></block><list></list></block></script></block-definition></blocks>