don't lookup empty stems after stripping the whole word

lucene/analysis/common/src/java/org/apache/lucene/analysis/hunspell/Stemmer.java

@@ -488,6 +488,8 @@ final class Stemmer {
     int stripEnd = dictionary.stripOffsets[stripOrd + 1];
     int stripLen = stripEnd - stripStart;
 
+    if (stripLen + deAffixedLen == 0) return null;
+
     char[] stripData = dictionary.stripData;
     int condition = dictionary.getAffixCondition(affix);
     if (condition != 0) {

lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/TestFullStrip.java

@@ -26,5 +26,7 @@ public class TestFullStrip extends StemmerTestBase {
 
   public void testStemming() {
     assertStemsTo("tasty", "beer");
+    assertStemsTo("as", "a");
+    assertStemsTo("s");
   }
 }

lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/fullstrip.aff

@@ -4,3 +4,6 @@ FULLSTRIP
 
 SFX A Y 1
 SFX A   beer        tasty  .
+
+SFX S Y 1
+SFX S	0	s	.

lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/fullstrip.dic

@@ -1,2 +1,3 @@
-1
+2
 beer/A
+a/S