Return FALSE on seek past EOF (#7324)

Fixes #7323

While I'm not a fan, the Arduino FileSeek API online shows that a seek()
past EOF should return FALSE.
https://www.arduino.cc/en/Reference/FileSeek

SPIFFS and SDFS obey this, but LittleFS followed the POSIX standard or
allowing seeks past EOF.

Update LittleFS::seek() to follow the Arduino API and add tests for it.

libraries/LittleFS/src/LittleFS.h

@@ -377,11 +377,16 @@ class LittleFSFileImpl : public FileImpl
         if (mode == SeekEnd) {
             offset = -offset; // TODO - this seems like its plain wrong vs. POSIX
         }
+        auto lastPos = position();
         int rc = lfs_file_seek(_fs->getFS(), _getFD(), offset, (int)mode); // NB. SeekMode === LFS_SEEK_TYPES
         if (rc < 0) {
             DEBUGV("lfs_file_seek rc=%d\n", rc);
             return false;
         }
+        if (position() > size()) {
+            seek(lastPos, SeekSet); // Pretend the seek() never happened
+            return false;
+        }
         return true;
     }
 

tests/host/fs/test_fs.inc

@@ -174,6 +174,30 @@ TEST_CASE(TESTPRE "open(w+) truncates file", TESTPAT)
     REQUIRE( t == "");
 }
 
+TEST_CASE(TESTPRE "peek() returns -1 on EOF", TESTPAT)
+{
+    FS_MOCK_DECLARE(64, 8, 512, "");
+    REQUIRE(FSTYPE.begin());
+    createFile("/file1", "some text");
+    auto f = FSTYPE.open("/file1", "r+");
+    REQUIRE(f.seek(8));
+    REQUIRE(f.peek() == 't');
+    REQUIRE(f.read() == 't');
+    REQUIRE(f.peek() == -1);
+    REQUIRE(f.read() == -1);
+    f.close();
+}
+
+TEST_CASE(TESTPRE "seek() pase EOF returns error (#7323)", TESTPAT)
+{
+    FS_MOCK_DECLARE(64, 8, 512, "");
+    REQUIRE(FSTYPE.begin());
+    createFile("/file1", "some text");
+    auto f = FSTYPE.open("/file1", "r+");
+    REQUIRE_FALSE(f.seek(10));
+    f.close();
+}
+
 #ifdef FS_HAS_DIRS
 
 #if FSTYPE != SDFS