Don't silently swallow unclosed tag content; propagate for error handling instead

[srowen]

See #436 (comment) for context. This stops silently swallowing unclosed tags at the end of input and instead propagates the remaining content for normal error handling.

Closes #436

[srowen]

CC @HyukjinKwon in case you're interested

[codecov-io]

Codecov Report

Merging #437 into master will increase coverage by 0.39%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #437      +/-   ##
==========================================
+ Coverage   88.46%   88.86%   +0.39%     
==========================================
  Files          17       17              
  Lines         806      808       +2     
  Branches       71       75       +4     
==========================================
+ Hits          713      718       +5     
+ Misses         93       90       -3

Impacted Files	Coverage Δ
...m/databricks/spark/xml/parsers/StaxXmlParser.scala	97.63% <100%> (+0.03%)	⬆️
...cala/com/databricks/spark/xml/XmlInputFormat.scala	93.28% <100%> (+0.74%)	⬆️
...la/com/databricks/spark/xml/util/InferSchema.scala	89.72% <0%> (+1.36%)	⬆️

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[HyukjinKwon]

LGTM. Thanks @srowen for fixing this.