Fix NPE in RebaseTodoFile#parseComments

Change-Id: I5487f3c2609eaf2a0ddf71ebb2f6c9701fb7600c
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit/src/org/eclipse/jgit/lib/RebaseTodoFile.java

@@ -137,12 +137,14 @@ public class RebaseTodoFile {
 			if (skip != -1) {
 				// try to parse the line as non-comment
 				line = parseLine(buf, skip, lineEnd);
+				if (line != null) {
 					// successfully parsed as non-comment line
 					// mark this line as a comment explicitly
 					line.setAction(Action.COMMENT);
 					// use the read line as comment string
 					line.setComment(commentString);
 				}
+			}
 		} catch (Exception e) {
 			// parsing as non-comment line failed
 			line = null;