Search bigrams for the lower case version of the word (A46)

...if there aren't any for the exact case version.

Bug: 6752830
Change-Id: I2737148b01ba04a64febe009ceb2ef53c265d224
diff --git a/native/jni/src/char_utils.h b/native/jni/src/char_utils.h
index 607dc51..21dca9a 100644
--- a/native/jni/src/char_utils.h
+++ b/native/jni/src/char_utils.h
@@ -50,8 +50,7 @@
     return c;
 }
 
-inline static unsigned short toBaseLowerCase(unsigned short c) {
-    c = toBaseChar(c);
+inline static unsigned short toLowerCase(const unsigned short c) {
     if (isAsciiUpper(c)) {
         return toAsciiLower(c);
     } else if (isAscii(c)) {
@@ -60,6 +59,10 @@
     return latin_tolower(c);
 }
 
+inline static unsigned short toBaseLowerCase(const unsigned short c) {
+    return toLowerCase(toBaseChar(c));
+}
+
 } // namespace latinime
 
 #endif // LATINIME_CHAR_UTILS_H