Fix another PepDB NPE from the crawler

[labkey-jeckels]

Rationale

ERROR ExceptionUtil            2025-04-03T02:47:28,275    http-nio-8111-exec-10 : Unhandled exception: Cannot invoke "java.lang.CharSequence.length()" because "this.text" is null
java.lang.NullPointerException: Cannot invoke "java.lang.CharSequence.length()" because "this.text" is null
	at java.base/java.util.regex.Matcher.getTextLength(Matcher.java:1769) ~[?:?]
	at java.base/java.util.regex.Matcher.reset(Matcher.java:415) ~[?:?]
	at java.base/java.util.regex.Matcher.<init>(Matcher.java:252) ~[?:?]
	at java.base/java.util.regex.Pattern.matcher(Pattern.java:1134) ~[?:?]
	at org.labkey.api.data.ExcelWriter.cleanSheetName(ExcelWriter.java:308) ~[api-25.4-SNAPSHOT.jar:?]
	at org.labkey.api.data.ExcelWriter.setSheetName(ExcelWriter.java:301) ~[api-25.4-SNAPSHOT.jar:?]
	at org.scharp.atlas.pepdb.PepDBController$PeptideExcelExportAction.printExcel(PepDBController.java:854) ~[pepdb-25.4-SNAPSHOT.jar:?]
	at org.scharp.atlas.pepdb.PepDBController$PeptideDefaultExcelExportAction.export(PepDBController.java:898) ~[pepdb-25.4-SNAPSHOT.jar:?]
	at org.labkey.api.action.ExportAction.getView(ExportAction.java:52) ~[api-25.4-SNAPSHOT.jar:?]
	at org.labkey.api.action.SimpleViewAction.handleRequest(SimpleViewAction.java:75) ~[api-25.4-SNAPSHOT.jar:?]

Changes

• Use a default message value
• Lots of minor code cleanup