Fix a bunch of sign mismatch warnings.

core/src/fxge/ge/fx_ge_linux.cpp

Index: core/src/fxge/ge/fx_ge_linux.cpp
diff --git a/core/src/fxge/ge/fx_ge_linux.cpp b/core/src/fxge/ge/fx_ge_linux.cpp
index 065fd124bba0ddffd9af7771451aef5544fc8df6..a03cd814510ab1ed15705ecf19e2b7dd100f5336 100644
--- a/core/src/fxge/ge/fx_ge_linux.cpp
+++ b/core/src/fxge/ge/fx_ge_linux.cpp
@@ -120,7 +120,7 @@ void* CFX_LinuxFontInfo::MapFont(int weight,
       }
     } break;
     case FXFONT_GB2312_CHARSET: {
-      for (int32_t i = 0; i < FX_ArraySize(g_LinuxGbFontList); ++i) {
+      for (size_t i = 0; i < FX_ArraySize(g_LinuxGbFontList); ++i) {
         auto it = m_FontList.find(g_LinuxGbFontList[i]);
         if (it != m_FontList.end()) {
           return it->second;
@@ -128,7 +128,7 @@ void* CFX_LinuxFontInfo::MapFont(int weight,
       }
     } break;
     case FXFONT_CHINESEBIG5_CHARSET: {
-      for (int32_t i = 0; i < FX_ArraySize(g_LinuxB5FontList); ++i) {
+      for (size_t i = 0; i < FX_ArraySize(g_LinuxB5FontList); ++i) {
         auto it = m_FontList.find(g_LinuxB5FontList[i]);
         if (it != m_FontList.end()) {
           return it->second;
@@ -136,7 +136,7 @@ void* CFX_LinuxFontInfo::MapFont(int weight,
       }
     } break;
     case FXFONT_HANGEUL_CHARSET: {
-      for (int32_t i = 0; i < FX_ArraySize(g_LinuxHGFontList); ++i) {
+      for (size_t i = 0; i < FX_ArraySize(g_LinuxHGFontList); ++i) {
         auto it = m_FontList.find(g_LinuxHGFontList[i]);
         if (it != m_FontList.end()) {
           return it->second;