Fix incorrect uses of getpwuid_r()

The function's behavior was recently fixed to succeed, but return a NULL
pointer, when the entry was not found. Fixes a crash in this case.

src/apps/terminal/Shell.cpp

@@ -400,8 +400,9 @@ Shell::_Spawn(int row, int col, const ShellParameters& parameters)
 	char stringBuffer[256];
 
 	if (argv == NULL || argc == 0) {
-		if (!getpwuid_r(getuid(), &passwdStruct, stringBuffer,
+		if (getpwuid_r(getuid(), &passwdStruct, stringBuffer,
-				sizeof(stringBuffer), &passwdResult)) {
+				sizeof(stringBuffer), &passwdResult) == 0
+			&& passwdResult != NULL) {
 			defaultArgs[0] = passwdStruct.pw_shell;
 		}
 

src/system/libroot/os/find_directory.cpp

@@ -381,7 +381,8 @@ find_directory(directory_which which, dev_t device, bool createIt,
 				struct passwd *pw;
 
 				if (getpwuid_r(geteuid(), &pwBuffer, pwStringBuffer,
-						sizeof(pwStringBuffer), &pw) == 0) {
+						sizeof(pwStringBuffer), &pw) == 0
+					&& pw != NULL) {
 					home = pw->pw_dir;
 				}
 #endif	// USE_PWENTS