PrairieMetadata: fix critical errors

This change fixes several metadata parsing bugs:

1) The relevant XML element is called "SubindexedValue", not
   "SubindexValue". Without this change, subindexed values are never
   read correctly, so e.g. X/Y/Z stage positions are not parsed.

2) The loop variable for subindexed values is "s", not "i".
   Without this change, an NPE is typically thrown during the
   SubindexedValues parsing loop.

3) Subindexed value table should be indexed on subindex, not index.

4) Parsing of subindexed values from old-style XML (<Key> elements)
   did not add the parsed subindexed value table to the data structure.

components/formats-gpl/src/loci/formats/in/PrairieMetadata.java

@@ -320,6 +320,7 @@ private void parseKeys(final Element el, final ValueTable table) {
           for (int i=0; i<tokens.length; i++) {
             subSubTable.put("" + i, new ValueItem(tokens[i], null));
           }
+          subTable.put(index, subSubTable);
         }
       }
     }
@@ -377,16 +378,16 @@ private void parsePVStateShard(final Element el, final ValueTable table) {
         if (index == null) continue; // invalid <SubindexedValues> element
         final ValueTable subSubTable = new ValueTable();
         subTable.put(index, subSubTable);
-        // iterate over <SubindexValue> children
+        // iterate over <SubindexedValue> children
         final NodeList subNodes =
-          sivElement.getElementsByTagName("SubindexValue");
+          sivElement.getElementsByTagName("SubindexedValue");
         for (int s = 0; s < subNodes.getLength(); s++) {
-          final Element subElement = el(subNodes, i);
+          final Element subElement = el(subNodes, s);
           final String subindex = attr(subElement, "subindex");
           if (subindex == null) continue; // invalid <SubindexedValue> element
           final String sValue = attr(subElement, "value");
           final String sDescription = attr(subElement, "description");
-          subSubTable.put(index, new ValueItem(sValue, sDescription));
+          subSubTable.put(subindex, new ValueItem(sValue, sDescription));
         }
       }
     }