[libzstd] Fix ZSTD_decompressBound() on bad skippable frames

The function didn't verify that the skippable frame size is correct.

lib/legacy/zstd_legacy.h

@@ -238,6 +238,10 @@ MEM_STATIC ZSTD_frameSizeInfo ZSTD_findFrameSizeInfoLegacy(const void *src, size
             frameSizeInfo.decompressedBound = ZSTD_CONTENTSIZE_ERROR;
             break;
     }
+    if (frameSizeInfo.compressedSize > srcSize) {
+        frameSizeInfo.compressedSize = ERROR(srcSize_wrong);
+        frameSizeInfo.decompressedBound = ZSTD_CONTENTSIZE_ERROR;
+    }
     return frameSizeInfo;
 }