[LLD][COFF] Keep hasData true in NullChunk constructor

NullChunk instances do write data, even if it's always zero. Setting hasData to false
causes Writer::assignAddresses to ignore them when calculating rawSize. This usually
isn't an issue, as null chunks are typically in the middle of a section and later
chunks adjust the size. However, on ARM64EC, the auxiliary IAT is placed at the end
of the .rdata section and ends with a null chunk, making this problematic.

Author: cjacek

lld/COFF/DLL.cpp

@@ -132,7 +132,6 @@ class ImportDirectoryChunk : public NonSectionChunk {
 class NullChunk : public NonSectionChunk {
 public:
   explicit NullChunk(size_t n, uint32_t align) : size(n) {
-    hasData = false;
     setAlignment(align);
   }
   explicit NullChunk(COFFLinkerContext &ctx)

lld/test/COFF/arm64ec-import.test

@@ -160,6 +160,19 @@ BASERELOC-NEXT:     Type: DIR64
 BASERELOC-NEXT:     Address: 0x5020
 BASERELOC-NEXT:   }
 
+
+Build with -filealign:8 to enable precise size checking.
+
+RUN: lld-link -machine:arm64ec -dll -noentry -out:out-size.dll loadconfig-arm64ec.obj icall.obj hybmp.obj \
+RUN:          test.obj test-arm64ec.lib test2-arm64ec.lib -filealign:8
+
+RUN: llvm-readobj --headers out-size.dll | FileCheck --check-prefix=RDATA-HEADER %s
+
+RDATA-HEADER:      Name: .rdata (2E 72 64 61 74 61 00 00)
+RDATA-HEADER-NEXT: VirtualSize: 0x2030
+RDATA-HEADER-NEXT: VirtualAddress: 0x3000
+RDATA-HEADER-NEXT: RawDataSize: 8240
+
 #--- test.s
     .section .test, "r"
     .globl arm64ec_data_sym