DataHandle: fix findString(..) and support handles with unknown length

- The findString(..) method used to require the exact length of the
	handle, this length can be unknown, e.g. for compressed handles.
	This is	no longer the case

Author: gab1one

src/main/java/org/scijava/io/handle/DataHandle.java

@@ -366,7 +366,10 @@ default String findString(final boolean saveString, final int blockSize,
 			new DataHandleInputStream<>(this), getEncoding());
 		final char[] buf = new char[blockSize];
 		long loc = 0;
-		while (loc < maxLen && offset() < length() - 1) {
+		int r = 0;
+
+		// NB: we need at least 2 bytes to read a char
+		while (loc < maxLen && ((r = in.read(buf, 0, blockSize)) > 1)) { 
 			// if we're not saving the string, drop any old, unnecessary output
 			if (!saveString) {
 				final int outLen = out.length();
@@ -378,16 +381,12 @@ default String findString(final boolean saveString, final int blockSize,
 					bytesDropped += dropIndex;
 				}
 			}
-
-			// read block from stream
-			final int r = in.read(buf, 0, blockSize);
-			if (r <= 0) throw new IOException("Cannot read from stream: " + r);
-
 			// append block to output
 			out.append(buf, 0, r);
 
 			// check output, returning smallest possible string
-			int min = Integer.MAX_VALUE, tagLen = 0;
+			int min = Integer.MAX_VALUE;
+			int tagLen = 0;
 			for (final String t : terminators) {
 				final int len = t.length();
 				final int start = (int) (loc - bytesDropped - len);