rest: improve error when only header of a block is available.

This avoids calling ReadRawBlockFromDisk() when the block is expected
not to be available because we haven't downloaded it yet and only know
the header.

Author: mzumsande

src/rest.cpp

@@ -309,8 +309,11 @@ static bool rest_block(const std::any& context,
         if (!pblockindex) {
             return RESTERR(req, HTTP_NOT_FOUND, hashStr + " not found");
         }
-        if (chainman.m_blockman.IsBlockPruned(*pblockindex)) {
-            return RESTERR(req, HTTP_NOT_FOUND, hashStr + " not available (pruned data)");
+        if (!(pblockindex->nStatus & BLOCK_HAVE_DATA)) {
+            if (chainman.m_blockman.IsBlockPruned(*pblockindex)) {
+                return RESTERR(req, HTTP_NOT_FOUND, hashStr + " not available (pruned data)");
+            }
+            return RESTERR(req, HTTP_NOT_FOUND, hashStr + " not available (not fully downloaded)");
         }
         pos = pblockindex->GetBlockPos();
     }