Cherry-pick: ICU-21793 Fix ucptrietest golden diff

Upstream commit: https://github.com/unicode-org/icu/commit/698efda42bb21a9da1c92348d3e73466c8a528fe

Bug: 213284403
Test: Push the test binary onto the device and run the following command
  ./cintltst64 -w /tsutil/ucptrietest/TrieTestSet1
Change-Id: Ib03ae93aa8638f1a1e68d639e5eaf9fe92a5781f

1 files changed, 7 insertions, 6 deletions

diff --git a/icu4c/source/tools/toolutil/toolutil.cpp b/icu4c/source/tools/toolutil/toolutil.cpp
index 1fc68aa69..a9dc37377 100644
--- a/icu4c/source/tools/toolutil/toolutil.cpp
+++ b/icu4c/source/tools/toolutil/toolutil.cpp
@@ -228,18 +228,19 @@ uprv_compareGoldenFiles(
     std::ifstream ifs(goldenFilePath, std::ifstream::in);
     int32_t pos = 0;
     char c;
-    while ((c = ifs.get()) != std::char_traits<char>::eof() && pos < bufferLen) {
+    while (ifs.get(c) && pos < bufferLen) {
         if (c != buffer[pos]) {
             // Files differ at this position
-            return pos;
+            break;
         }
         pos++;
     }
-    if (pos < bufferLen || c != std::char_traits<char>::eof()) {
-        // Files are different lengths
-        return pos;
+    if (pos == bufferLen && ifs.eof()) {
+        // Files are same lengths
+        pos = -1;
     }
-    return -1;
+    ifs.close();
+    return pos;
 }
 
 /*U_CAPI UDate U_EXPORT2