chore: Apply suggestions from code review

Author: hamzaremmal

Diff for: compiler/src/dotty/tools/io/Jar.scala

@@ -50,7 +50,7 @@ class Jar(file: File) {
   def mainClass: Option[String]     = manifest.map(_(Name.MAIN_CLASS))
   /** The manifest-defined classpath String if available. */
   def classPathString: Option[String] =
-    for (m <- manifest ; cp <- m.attrs.get(Name.CLASS_PATH) if !cp.isBlank()) yield cp
+    for (m <- manifest ; cp <- m.attrs.get(Name.CLASS_PATH) if !cp.trim().isEmpty()) yield cp
   def classPathElements: List[String] = classPathString match {
     case Some(s)  => s.split("\\s+").toList
     case _        => Nil