graphics: initialize count to 0 in initCapabilities

Be more defensive against HALs that do not initialize count.

Test: manual
Change-Id: I8b70454a1a3134c01d225be504579fc2e81ca88b
diff --git a/graphics/allocator/2.0/default/Gralloc.cpp b/graphics/allocator/2.0/default/Gralloc.cpp
index 3a102d1..0b9e863 100644
--- a/graphics/allocator/2.0/default/Gralloc.cpp
+++ b/graphics/allocator/2.0/default/Gralloc.cpp
@@ -131,7 +131,7 @@
 
 void GrallocHal::initCapabilities()
 {
-    uint32_t count;
+    uint32_t count = 0;
     mDevice->getCapabilities(mDevice, &count, nullptr);
 
     std::vector<Capability> caps(count);
diff --git a/graphics/mapper/2.0/default/GrallocMapper.cpp b/graphics/mapper/2.0/default/GrallocMapper.cpp
index 3b6460a..526aca2 100644
--- a/graphics/mapper/2.0/default/GrallocMapper.cpp
+++ b/graphics/mapper/2.0/default/GrallocMapper.cpp
@@ -127,7 +127,7 @@
 
 void GrallocMapperHal::initCapabilities()
 {
-    uint32_t count;
+    uint32_t count = 0;
     mDevice->getCapabilities(mDevice, &count, nullptr);
 
     std::vector<int32_t> caps(count);