hghave: fix possible int('') in has_clang_format()

tests/hghave.py

@@ -591,7 +591,7 b' def has_pylint():'
 
 @check("clang-format", "clang-format C code formatter")
 def has_clang_format():
-    m = matchoutput('clang-format --version', br'clang-format version (\d*)')
+    m = matchoutput('clang-format --version', br'clang-format version (\d+)')
     # style changed somewhere between 4.x and 6.x
     return m and int(m.group(1)) >= 6