join: correct java=true case

Author: scivision

+stdlib/join.m

@@ -32,7 +32,7 @@
 if stdlib.isoctave()
   p = javaObject("java.io.File", b).toPath().resolve(o).toString();
 elseif use_java
-  p = java.io.File(b).toPath().resolve(o);
+  p = string(java.io.File(b).toPath().resolve(o));
 else
 
 if startsWith(o, "/") || (ispc && stdlib.is_absolute(o))
@@ -45,3 +45,9 @@
 end
 
 end
+
+%!assert(join("", ""), "")
+%!assert(join("", "b"), "b")
+%!assert(join("a", ""), "a")
+%!assert(join("a", "b"), "a/b")
+%!assert(join("a", "/b/c"), "/b/c")

test/TestFilePure.m

@@ -26,7 +26,8 @@
 {"a/b/../", "c/d/../", "a/b/../c/d/.."}, ...
 {"a/b", "..", "a/b/.."}, ...
 {"a/b", "c/d", "a/b/c/d"}, ...
-{"ab/cd", "/ef", "/ef"} ...
+{"ab/cd", "/ef", "/ef"}, ...
+{matlabroot, "bin", matlabroot + "/bin"}
 }
 
 p_suffix = {{"", ""}, {"/a/b/c", ""}, {"/a/b/c/", ""}, {"a/b/c.txt", ".txt"}, {"a/b/c.txt.gz", ".gz"}, {".stat", ".stat"}, {".stat.txt", ".txt"}}