assert to prevent truncation bug regression

Author: frederic-mahe

src/showalign.cc

@@ -311,7 +311,6 @@ auto align_getrow(char const * seq, char const * cigar, int const alignlen, bool
     cursor += runlength;
   }
 
-  // assert(row[cursor] == '\0');  // is not always true?! (see issue 473 for a test)
-  row[cursor] = '\0';  // not already initialized to null?
+  assert(row[cursor] == '\0');
   return row;
 }