Cherry-pick: ICU-21449 Infinite loop can occur with locale IDs that c…

…ontain RES_PATH_SEPARATOR (#66)

This change cherry-picks the upstream fix for the issue of an infinite loop when calling various APIs with locale IDs that contain `RES_PATH_SEPARATOR`.

Upstream ticket:
https://unicode-org.atlassian.net/browse/ICU-21449

Upstream PR:
unicode-org/icu#1549

Detailed Description (from the upstream PR):
When calling APIs like `uloc_getDisplayLanguage`, if the input locale ID has `/` (the `RES_PATH_SEPARATOR` value) then the resource look-up code ends up in an infinite loop.

For example, the following code will never return:

```c++
UErrorCode status = U_ZERO_ERROR;
const char* localeNameTemp = "/"; // RES_PATH_SEPARATOR
uloc_getDisplayLanguage(localeNameTemp, localeNameTemp, NULL, 0, &status);
```

The `do {...} while` loop in `ures_getByKeyWithFallback` calls `res_findResource`, but it never checks to see if the returned resource is `RES_BOGUS`, meaning that for some paths it will never terminate. (Thanks to am11 for doing the initial investigation into this issue.)

This PR also includes a test case for the issue. Note that there is nothing really "tested" by the test case, as the test is to simply ensure that calling the API doesn't cause a hang due to the infinite loop.

icu/icu4c/source/common/uresbund.cpp

@@ -1908,6 +1908,8 @@ ures_getByKeyWithFallback(const UResourceBundle *resB,
                             } else {
                               break;
                             }
+                        } else if (res == RES_BOGUS) {
+                            break;
                         }
                     } while(*myPath); /* Continue until the whole path is consumed */
                 }

icu/icu4c/source/test/cintltst/cloctst.c

@@ -280,6 +280,7 @@ void addLocaleTest(TestNode** root)
     TESTCASE(TestBug20370);
     TESTCASE(TestBug20321UnicodeLocaleKey);
     TESTCASE(TestUsingDefaultWarning);
+    TESTCASE(TestBug21449InfiniteLoop);
 }
 
 
@@ -6980,11 +6981,12 @@ static void TestUsingDefaultWarning() {
         log_err("ERROR: in uloc_getDisplayKeywordValue %s %s return len:%d %s with status %d %s\n",
                 keyword_value, keyword, length, errorOutputBuff, status, myErrorName(status));
       }
-}      
+}
+
 // Test case for ICU-20575
 // This test checks if the environment variable LANG is set, 
 // and if so ensures that both C and C.UTF-8 cause ICU's default locale to be en_US_POSIX.
-static void TestCDefaultLocale(){
+static void TestCDefaultLocale() {
     const char *defaultLocale = uloc_getDefault();
     char *env_var = getenv("LANG");
     if (env_var == NULL) {
@@ -6995,3 +6997,13 @@ static void TestCDefaultLocale(){
       log_err("The default locale for LANG=%s should be en_US_POSIX, not %s\n", env_var, defaultLocale);
     }
 }
+
+// Test case for ICU-21449
+static void TestBug21449InfiniteLoop() {
+    UErrorCode status = U_ZERO_ERROR;
+    const char* invalidLocaleId = RES_PATH_SEPARATOR_S;
+
+    // The issue causes an infinite loop to occur when looking up a non-existent resource for the invalid locale ID,
+    // so the test is considered passed if the call to the API below returns anything at all.
+    uloc_getDisplayLanguage(invalidLocaleId, invalidLocaleId, NULL, 0, &status);
+}

icu/icu4c/source/test/cintltst/cloctst.h

@@ -142,7 +142,7 @@ static void TestToUnicodeLocaleType(void);
 static void TestToLegacyType(void);
 static void TestBug20149(void);
 static void TestCDefaultLocale(void);
-
+static void TestBug21449InfiniteLoop(void);
 
 /**
  * U_USING_DEFAULT_WARNING