Catch IndentationError in isidentifier()

Fixes:

    >>> from hy._compat import isidentifier
    >>> isidentifier(u"  0\n 0")
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      File "hy/_compat.py", line 47, in isidentifier
        tokens = list(T.generate_tokens(StringIO(x).readline))
      File "/usr/lib/python2.7/tokenize.py", line 374, in generate_tokens
        ("<tokenize>", lnum, pos, line))
      File "<tokenize>", line 2
        0
        ^
    IndentationError: unindent does not match any outer indentation level

NEWS.rst

@@ -30,6 +30,7 @@ Bug Fixes
   objects.
 * Fixed errors from `from __future__ import ...` statements and missing Hy
   module docstrings caused by automatic importing of Hy builtins.
+* Fixed crash in `mangle` for some pathological inputs
 
 0.15.0
 ==============================

hy/_compat.py

@@ -45,7 +45,7 @@ def isidentifier(x):
     from io import StringIO
     try:
         tokens = list(T.generate_tokens(StringIO(x).readline))
-    except T.TokenError:
+    except (T.TokenError, IndentationError):
         return False
     return len(tokens) == 2 and tokens[0][0] == T.NAME
 

tests/native_tests/mangling.hy

@@ -157,3 +157,7 @@
                ["⚘-⚘" "hyx_XflowerX_XflowerX"]]]
     (assert (= (mangle a) b))
     (assert (= (unmangle b) a))))
+
+(defn test-mangle-bad-indent []
+  ; Shouldn't crash with IndentationError
+  (mangle "  0\n 0"))