Fix bug in test spec parser handling of escaping in ORed patterns

It did not clear out all of its internal state when switching from
one pattern to another, so when it should've escaped `,`, it took
its position from its position in the original user-provided string,
rather than its position in the current pattern.

Fixes #1905

include/internal/catch_test_spec_parser.cpp

@@ -168,6 +168,7 @@ namespace Catch {
          m_pos = m_arg.size();
          m_substring.clear();
          m_patternName.clear();
+         m_realPatternPos = 0;
          return false;
       }
       endMode();
@@ -186,6 +187,7 @@ namespace Catch {
         }
 
         m_patternName.clear();
+        m_realPatternPos = 0;
 
         return token;
     }